x11vnc(1) - Linux man page

Name

x11vnc - allow VNC connections to real X11 displays version: 0.9.3, lastmod: 2007-09-30

Synopsis

x11vnc [OPTION]...

Description

Typical usage is:

Run this command in a shell on the remote machine "far-host"

with X session you wish to view:

x11vnc -display :0

Then run this in another window on the machine you are sitting at:

vncviewer far-host:0

Once x11vnc establishes connections with the X11 server and starts listening as a VNC server it will print out a string: PORT=XXXX where XXXX is typically 5900 (the default VNC server port). One would next run something like this on the local machine: "vncviewer hostname:N" where "hostname" is the name of the machine running x11vnc and N is XXXX - 5900, i.e. usually "vncviewer hostname:0".

By default x11vnc will not allow the screen to be shared and it will exit as soon as the client disconnects. See -shared and -forever below to override these protections. See the FAQ for details how to tunnel the VNC connection through an encrypted channel such as ssh(1). In brief:

ssh -t -L 5900:localhost:5900 far-host 'x11vnc -localhost -display :0'

% vncviewer -encodings 'copyrect tight zrle hextile' localhost:0

Also, use of a VNC password (-rfbauth or -passwdfile) is strongly recommended.

For additional info see: http://www.karlrunge.com/x11vnc/ and http://www.karlrunge.com/x11vnc/#faq

Config file support: if the file $HOME/.x11vncrc exists then each line in it is treated as a single command line option. Disable with -norc. For each option name, the leading character "-" is not required. E.g. a line that is either "forever" or "-forever" may be used and are equivalent. Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines. The "#" character comments out to the end of the line in the usual way (backslash it for a literal). Leading and trailing whitespace is trimmed off. Lines may be continued with a "\" as the last character of a line (it becomes a space character).

Options

-display disp

X11 server display to connect to, usually :0. The X

server process must be running on same machine and support MIT-SHM. Equivalent to setting the DISPLAY environment variable to disp.

See the description below of the "-display WAIT:..."

extensions, where alias "-find" will find the user's display automatically, and "-create" will create a Xvfb session if no session is found.

-auth file

Set the X authority file to be file, equivalent to

setting the XAUTHORITY environment variable to file before startup. Same as -xauth file. See xsecurity(7) , xauth(1) man pages for more info.

-N

If the X display is :N, try to set the VNC display

to also be :N This just sets the -rfbport option to 5900+N. The program will exit immediately if that port is not available.

-autoport n

Automatically probe for a free VNC port starting at n.

The default is to start probing at 5900. Use this to stay away from other VNC servers near 5900.

-reflect host:N

Instead of connecting to and polling an X display,

connect to the remote VNC server host:N and be a reflector/repeater for it. This is useful for trying to manage the case of many simultaneous VNC viewers (e.g. classroom broadcasting) where, e.g. you put a repeater on each network switch, etc, to improve performance by distributing the load and network traffic. Implies -shared (use -noshared as a later option to disable). See the discussion below under -rawfb vnc:host:N for more details.

-id windowid

Show the X window corresponding to windowid not

the entire display. New windows like popup menus, transient toplevels, etc, may not be seen or may be clipped. Disabling SaveUnders or BackingStore in the X server may help show them. x11vnc may crash if the window is initially partially obscured, changes size, is iconified, etc. Some steps are taken to avoid this and the -xrandr mechanism is used to track resizes. Use xwininfo(1) to get the window id, or use "-id pick" to have x11vnc run xwininfo(1) for you and extract the id. The -id option is useful for exporting very simple applications (e.g. the current view on a webcam).

-sid windowid

As -id, but instead of using the window directly it

shifts a root view to it: this shows SaveUnders menus, etc, although they will be clipped if they extend beyond the window.

-clip WxH+X+Y

Only show the sub-region of the full display that

corresponds to the rectangle geometry with size WxH and offset +X+Y. The VNC display has size WxH (i.e. smaller than the full display). This also works for -id/-sid mode where the offset is relative to the upper left corner of the selected window. An example use of this option would be to split a large (e.g. Xinerama) display into two parts to be accessed via separate viewers by running a separate x11vnc on each part.

-flashcmap

In 8bpp indexed color, let the installed colormap flash

as the pointer moves from window to window (slow). Also try the -8to24 option to avoid flash altogether.

-shiftcmap n

Rare problem, but some 8bpp displays use less than 256

colorcells (e.g. 16-color grayscale, perhaps the other bits are used for double buffering) *and* also need to shift the pixels values away from 0, .., ncells. n indicates the shift to be applied to the pixel values. To see the pixel values set DEBUG_CMAP=1 to print out a colormap histogram. Example: -shiftcmap 240

-notruecolor

For 8bpp displays, force indexed color (i.e. a colormap)

even if it looks like 8bpp TrueColor (rare problem).

-visual n

This option probably does not do what you think.

It simply *forces* the visual used for the framebuffer; this may be a bad thing... (e.g. messes up colors or cause a crash). It is useful for testing and for some workarounds. n may be a decimal number, or 0x hex. Run xdpyinfo(1) for the values. One may also use "TrueColor", etc. see <X11/X.h> for a list. If the string ends in ":m" then for better or for worse the visual depth is forced to be m.

-overlay

Handle multiple depth visuals on one screen, e.g. 8+24

and 24+8 overlay visuals (the 32 bits per pixel are packed with 8 for PseudoColor and 24 for TrueColor).

Currently -overlay only works on Solaris via

XReadScreen(3X11) and IRIX using XReadDisplay(3). On Solaris there is a problem with image "bleeding" around transient popup menus (but not for the menu itself): a workaround is to disable SaveUnders by passing the "-su" argument to Xsun (in /etc/dt/config/Xservers).

Use -overlay as a workaround for situations like these:

Some legacy applications require the default visual to be 8bpp (8+24), or they will use 8bpp PseudoColor even when the default visual is depth 24 TrueColor (24+8). In these cases colors in some windows will be incorrect in x11vnc unless -overlay is used. Another use of -overlay is to enable showing the exact mouse cursor shape (details below).

Under -overlay, performance will be somewhat slower

due to the extra image transformations required. For optimal performance do not use -overlay, but rather configure the X server so that the default visual is depth 24 TrueColor and try to have all apps use that visual (e.g. some apps have -use24 or -visual options).

-overlay_nocursor

Sets -overlay, but does not try to draw the exact mouse

cursor shape using the overlay mechanism.

-8to24 [opts]

Try this option if -overlay is not supported on your

OS, and you have a legacy 8bpp app that you want to view on a multi-depth display with default depth 24 (and is 32 bpp) OR have a default depth 8 display with depth 24 overlay windows for some apps. This option may not work on all X servers and hardware (tested on XFree86/Xorg mga driver and Xsun). The "opts" string is not required and is described below.

This mode enables a hack where x11vnc monitors windows

within 3 levels from the root window. If it finds any that are 8bpp it extracts the indexed color pixel values using XGetImage() and then applies a transformation using the colormap(s) to create TrueColor RGB values that it in turn inserts into bits 1-24 of the framebuffer. This creates a depth 24 "view" of the display that is then exported via VNC.

Conversely, for default depth 8 displays, the depth

24 regions are read by XGetImage() and everything is transformed and inserted into a depth 24 TrueColor framebuffer.

Note that even if there are *no* depth 24 visuals or

windows (i.e. pure 8bpp), this mode is potentially an improvement over -flashcmap because it avoids the flashing and shows each window in the correct color.

This method appear to work, but may still have bugs

and it does hog resources. If there are multiple 8bpp windows using different colormaps, one may have to iconify all but one for the colors to be correct.

There may be painting errors for clipping and switching

between windows of depths 8 and 24. Heuristics are applied to try to minimize the painting errors. One can also press 3 Alt_L's in a row to refresh the screen if the error does not repair itself. Also the option -fixscreen 8=3.0 or -fixscreen V=3.0 may be used to periodically refresh the screen at the cost of bandwidth (every 3 sec for this example).

The [opts] string can contain the following settings.

Multiple settings are separated by commas.

For for some X servers with default depth 24 a

speedup may be achieved via the option "nogetimage". This enables a scheme were XGetImage() is not used to retrieve the 8bpp data. Instead, it assumes that the 8bpp data is in bits 25-32 of the 32bit X pixels. There is no requirement that the X server should put the data there for our poll requests, but some do and so the extra steps to retrieve it can be skipped. Tested with mga driver with XFree86/Xorg. For the default depth 8 case this option is ignored.

To adjust how often XGetImage() is used to poll the

non-default visual regions for changes, use the option "poll=t" where "t" is a floating point time. (default: 0.05)

Setting the option "level2" will limit the search

for non-default visual windows to two levels from the root window. Do this on slow machines where you know the window manager only imposes one extra window between the app window and the root window.

Also for very slow machines use "cachewin=t"

where t is a floating point amount of time to cache XGetWindowAttributes results. E.g. cachewin=5.0. This may lead to the windows being unnoticed for this amount of time when deiconifying, painting errors, etc.

While testing on a very old SS20 these options gave

tolerable response: -8to24 poll=0.2,cachewin=5.0. For this machine -overlay is supported and gives better response.

Debugging for this mode can be enabled by setting

"dbg=1", "dbg=2", or "dbg=3".

-24to32

Very rare problem: if the framebuffer (X display

or -rawfb) is 24bpp instead of the usual 32bpp, then dynamically transform the pixels to 32bpp. This will be slower, but can be used to work around problems where VNC viewers cannot handle 24bpp (e.g. "main: setPF: not 8, 16 or 32 bpp?"). See the FAQ for more info.

In the case of -rawfb mode, the pixels are directly

modified by inserting a 0 byte to pad them out to 32bpp. For X displays, a kludge is done that is equivalent to "-noshm -visual TrueColor:32". (If better performance is needed for the latter, feel free to ask).

-scale fraction

Scale the framebuffer by factor fraction. Values

less than 1 shrink the fb, larger ones expand it. Note: image may not be sharp and response may be slower. If fraction contains a decimal point "." it is taken as a floating point number, alternatively the notation "m/n" may be used to denote fractions exactly, e.g. -scale 2/3

Scaling Options: can be added after fraction via

":", to supply multiple ":" options use commas. If you just want a quick, rough scaling without blending, append ":nb" to fraction (e.g. -scale 1/3:nb). No blending is the default for 8bpp indexed color, to force blending for this case use ":fb".

To disable -scrollcopyrect and -wirecopyrect under

-scale use ":nocr". If you need to to enable them use ":cr" or specify them explicitly on the command line. If a slow link is detected, ":nocr" may be applied automatically. Default: :cr

More esoteric options: for compatibility with vncviewers

the scaled width is adjusted to be a multiple of 4: to disable this use ":n4". ":in" use interpolation scheme even when shrinking, ":pad" pad scaled width and height to be multiples of scaling denominator (e.g. 3 for 2/3).

-scale_cursor frac

By default if -scale is supplied the cursor shape is

scaled by the same factor. Depending on your usage, you may want to scale the cursor independently of the screen or not at all. If you specify -scale_cursor the cursor will be scaled by that factor. When using -scale mode to keep the cursor at its "natural" size use "-scale_cursor 1". Most of the ":" scaling options apply here as well.

-viewonly

All VNC clients can only watch (default off).

-shared

VNC display is shared, i.e. more than one viewer can

connect at the same time (default off).

-once

Exit after the first successfully connected viewer

disconnects, opposite of -forever. This is the Default.

-forever

Keep listening for more connections rather than exiting

as soon as the first client(s) disconnect. Same as -many

-loop

Create an outer loop restarting the x11vnc process

whenever it terminates. -bg and -inetd are ignored in this mode (however see -loopbg below).

Useful for continuing even if the X server terminates

and restarts (at that moment the process will need permission to reconnect to the new X server of course).

Use, e.g., -loop100 to sleep 100 millisecs between

restarts, etc. Default is 2000ms (i.e. 2 secs) Use, e.g. -loop300,5 to sleep 300 ms and only loop 5 times.

If -loopbg (plus any numbers) is specified instead,

the "-bg" option is implied and the mode approximates inetd(8) usage to some degree. In this case when it goes into the background any listening sockets (i.e. ports 5900, 5800) are closed, so the next one in the loop can use them. This mode will only be of use if a VNC client (the only client for that process) is already connected before the process goes into the background, for example, usage of -display WAIT:.., -svc, and -connect can make use of this "poor man's" inetd mode. The default wait time is 500ms in this mode. This usage could use useful: -svc -loopbg

-timeout n

Exit unless a client connects within the first n seconds

after startup.

-sleepin n

At startup sleep n seconds before proceeding (e.g. to

allow redirs and listening clients to start up)

-inetd

Launched by

inetd(8): stdio instead of listening socket. Note: if you are not redirecting stderr to a log file (via shell 2> or -o option) you MUST also specify the -q option, otherwise the stderr goes to the viewer which will cause it to abort. Specifying both -inetd and -q and no -o will automatically close the stderr.

-tightfilexfer

Enable the TightVNC file transfer extension. Note that

that when the -viewonly option is supplied all file transfers are disabled. Also clients that log in viewonly cannot transfer files. However, if the remote control mechanism is used to change the global or per-client viewonly state the filetransfer permissions will NOT change.

IMPORTANT: please understand if -tightfilexfer is

specified and you run x11vnc as root for, say, inetd or display manager (gdm, kdm, ...) access and you do not have it switch users via the -users option, then VNC Viewers that connect are able to do filetransfer reads and writes as *root*.

Also, tightfilexfer is disabled in -unixpw mode.

-ultrafilexfer

Note: to enable UltraVNC filetransfer and to get it to

work you probably need to supply these libvncserver options: "-rfbversion 3.6 -permitfiletransfer" "-ultrafilexfer" is an alias for this combination.

IMPORTANT: please understand if -ultrafilexfer is

specified and you run x11vnc as root for, say, inetd or display manager (gdm, kdm, ...) access and you do not have it switch users via the -users option, then VNC Viewers that connect are able to do filetransfer reads and writes as *root*.

Note that sadly you cannot do both -tightfilexfer and

-ultrafilexfer at the same time because the latter requires setting the version to 3.6 and tightvnc will not do filetransfer when it sees that version number.

-http

Instead of using -httpdir (see below) to specify

where the Java vncviewer applet is, have x11vnc try to *guess* where the directory is by looking relative to the program location and in standard locations (/usr/local/share/x11vnc/classes, etc). Under -ssl or -stunnel the ssl classes subdirectory is sought.

-http_ssl

As -http, but force lookup for ssl classes subdir.

-avahi

Use the Avahi/mDNS ZeroConf protocol to advertize

this VNC server to the local network. (Related terms: Rendezvous, Bonjour). Depending on your setup, you may need to start avahi-daemon and open udp port 5353 in your firewall.

-mdns

Same as -avahi.

-connect string

For use with "vncviewer -listen" reverse connections.

If string has the form "host" or "host:port" the connection is made once at startup.

Use commas for a list of host's and host:port's.

E.g. -connect host1,host2 or host1:0,host2:5678. Note that to reverse connect to multiple hosts at the same time you will likely need to also supply: -shared

Note that unlike most vnc servers, x11vnc will require a

password for reverse as well as for forward connections. (provided password auth has been enabled, -rfbauth, etc) If you do not want to require a password for reverse connections set X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in your environment before starting x11vnc.

If string contains "/" it is instead interpreted

as a file to periodically check for new hosts. The first line is read and then the file is truncated. Be careful about the location of this file if x11vnc is running as root (e.g. via gdm(1) , etc).

-connect_or_exit str

As with -connect, except if none of the reverse

connections succeed, then x11vnc shutdowns immediately.

If you do not want x11vnc to listen on ANY interface

use -rfbport 0

-vncconnect, -novncconnect

Monitor the VNC_CONNECT X property set by the standard

VNC program vncconnect(1). When the property is set to "host" or "host:port" establish a reverse connection. Using xprop(1) instead of vncconnect may work (see the FAQ). The -remote control mechanism uses X11VNC_REMOTE channel, and this option disables/enables it as well. Default: -vncconnect

-allow host1[,host2..]

Only allow client connections from hosts matching

the comma separated list of hostnames or IP addresses. Can also be a numerical IP prefix, e.g. "192.168.100." to match a simple subnet, for more control build libvncserver with libwrap support (See the FAQ). If the list contains a "/" it instead is a interpreted as a file containing addresses or prefixes that is re-read each time a new client connects. Lines can be commented out with the "#" character in the usual way.

-localhost

Basically the same as "-allow 127.0.0.1".

Note: if you want to restrict which network interface

x11vnc listens on, see the -listen option below. E.g. "-listen localhost" or "-listen 192.168.3.21". As a special case, the option "-localhost" implies "-listen localhost".

A rare case, but for non-localhost -listen usage, if

you use the remote control mechanism (-R) to change the -listen interface you may need to manually adjust the -allow list (and vice versa) to avoid situations where no connections (or too many) are allowed.

If you do not want x11vnc to listen on ANY interface

(evidently you are using -connect or -connect_or_exit, or plan to use remote control: -R connect:host), use -rfbport 0

-nolookup

Do not use gethostbyname() or gethostbyaddr() to look up

host names or IP numbers. Use this if name resolution is incorrectly set up and leads to long pauses as name lookups time out, etc.

-input string

Fine tuning of allowed user input. If string does

not contain a comma "," the tuning applies only to normal clients. Otherwise the part before "," is for normal clients and the part after for view-only clients. "K" is for Keystroke input, "M" for Mouse-motion input, "B" for Button-click input, "C" is for Clipboard input, and "F" is for File transfer (ultravnc only). Their presence in the string enables that type of input. E.g. "-input M" means normal users can only move the mouse and "-input KMBCF,M" lets normal users do anything and enables view-only users to move the mouse. This option is ignored when a global -viewonly is in effect (all input is discarded in that case).

-grabkbd

When VNC viewers are connected, attempt to the grab

the keyboard so a (non-malicious) user sitting at the physical display is not able to enter keystrokes. This method uses XGrabKeyboard(3X11) and so it is not secure and does not rule out the person at the physical display injecting keystrokes by flooding the server with them, grabbing the keyboard himself, etc. Some degree of cooperation from the person at the display is assumed. This is intended for remote help-desk or educational usage modes.

-grabptr

As -grabkbd, but for the mouse pointer using

XGrabPointer(3X11). Unfortunately due to the way the X server works, the mouse can still be moved around by the user at the physical display, but he will not be able to change window focus with it. Also some window managers that call XGrabServer(3X11) for resizes, etc, will act on the local user's input. Again, some degree of cooperation from the person at the display is assumed.

-grabalways

Apply both -grabkbd and -grabptr even when no VNC

viewers are connected. If you only want one of them, use the -R remote control to turn the other back on, e.g. -R nograbptr.

-viewpasswd string

Supply a 2nd password for view-only logins. The -passwd

(full-access) password must also be supplied.

-passwdfile filename

Specify the libvncserver password via the first line

of the file filename (instead of via -passwd on the command line where others might see it via ps(1) ).

See the descriptions below for how to supply multiple

passwords, view-only passwords, to specify external programs for the authentication, and other features.

If the filename is prefixed with "rm:" it will be

removed after being read. Perhaps this is useful in limiting the readability of the file. In general, the password file should not be readable by untrusted users (BTW: neither should the VNC -rfbauth file: it is NOT encrypted, only obscured with a fixed key).

If the filename is prefixed with "read:" it will

periodically be checked for changes and reread. It is guaranteed to be reread just when a new client connects so that the latest passwords will be used.

If filename is prefixed with "cmd:" then the

string after the ":" is run as an external command: the output of the command will be interpreted as if it were read from a password file (see below). If the command does not exit with 0, then x11vnc terminates immediately. To specify more than 1000 passwords this way set X11VNC_MAX_PASSWDS before starting x11vnc. The environment variables are set as in -accept.

Note that due to the VNC protocol only the first 8

characters of a password are used (DES key).

If filename is prefixed with "custom:" then a

custom password checker is supplied as an external command following the ":". The command will be run when a client authenticates. If the command exits with 0 the client is accepted, otherwise it is rejected. The environment variables are set as in -accept.

The standard input to the custom command will be a

decimal digit "len" followed by a newline. "len" specifies the challenge size and is usually 16 (the VNC spec). Then follows len bytes which is the random challenge string that was sent to the client. This is then followed by len more bytes holding the client's response (i.e. the challenge string encrypted via DES with the user password in the standard situation).

The "custom:" scheme can be useful to implement

dynamic passwords or to implement methods where longer passwords and/or different encryption algorithms are used. The latter will require customizing the VNC client as well. One could create an MD5SUM based scheme for example.

File format for -passwdfile:

If multiple non-blank lines exist in the file they are

all taken as valid passwords. Blank lines are ignored. Password lines may be "commented out" (ignored) if they begin with the charactor "#" or the line contains the string "__SKIP__". Lines may be annotated by use of the "__COMM__" string: from it to the end of the line is ignored. An empty password may be specified via the "__EMPTY__" string on a line by itself (note your viewer might not accept empty passwords).

If the string "__BEGIN_VIEWONLY__" appears on a

line by itself, the remaining passwords are used for viewonly access. For compatibility, as a special case if the file contains only two password lines the 2nd one is automatically taken as the viewonly password. Otherwise the "__BEGIN_VIEWONLY__" token must be used to have viewonly passwords. (tip: make the 3rd and last line be "__BEGIN_VIEWONLY__" to have 2 full-access passwords)

-unixpw [list]

Use Unix username and password authentication. x11vnc

uses the su(1) program to verify the user's password. [list] is an optional comma separated list of allowed Unix usernames. If the [list] string begins with the character "!" then the entire list is taken as an exclude list. See below for per-user options that can be applied.

A familiar "login:" and "Password:" dialog is

presented to the user on a black screen inside the vncviewer. The connection is dropped if the user fails to supply the correct password in 3 tries or does not send one before a 25 second timeout. Existing clients are view-only during this period.

If the first character received is "Escape" then the

unix username will not be displayed after "login:" as it is typed. This could be of use for VNC viewers that automatically type the username and password.

Since the detailed behavior of

su(1) can vary from OS to OS and for local configurations, test the mode carefully. x11vnc will attempt to be conservative and reject a login if anything abnormal occurs.

One case to note: FreeBSD and the other BSD's by

default it is impossible for the user running x11vnc to validate his *own* password via su(1) (commenting out the pam_self.so entry in /etc/pam.d/su eliminates this behavior). So the x11vnc login will always *FAIL* for this case (even when the correct password is supplied).

A possible workaround for this on *BSD would be to

start x11vnc as root with the "-users +nobody" option to immediately switch to user nobody where the su'ing will proceed normally.

Another source of potential problems are PAM modules

that prompt for extra info, e.g. password aging modules. These logins will fail as well even when the correct password is supplied.

**IMPORTANT**: to prevent the Unix password being sent

in *clear text* over the network, one of two schemes will be enforced: 1) the -ssl builtin SSL mode, or 2) require both -localhost and -stunnel be enabled.

Method 1) ensures the traffic is encrypted between

viewer and server. A PEM file will be required, see the discussion under -ssl below (under some circumstances a temporary one can be automatically generated).

Method 2) requires the viewer connection to appear

to come from the same machine x11vnc is running on (e.g. from a ssh -L port redirection). And that the -stunnel SSL mode be used for encryption over the network.(see the description of -stunnel below).

Note: as a convenience, if you

ssh(1) in and start x11vnc it will check if the environment variable SSH_CONNECTION is set and appears reasonable. If it does, then the -ssl or -stunnel requirement will be dropped since it is assumed you are using ssh for the encrypted tunnelling. -localhost is still enforced. Use -ssl or -stunnel to force SSL usage even if SSH_CONNECTION is set.

To override the above restrictions you can set

environment variables before starting x11vnc:

Set UNIXPW_DISABLE_SSL=1 to disable requiring either

-ssl or -stunnel. Evidently you will be using a different method to encrypt the data between the vncviewer and x11vnc: perhaps ssh(1) or an IPSEC VPN.

Note that use of -localhost with

ssh(1) is roughly the same as requiring a Unix user login (since a Unix password or the user's public key authentication is used by sshd on the machine where x11vnc runs and only local connections from that machine are accepted).

Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost

requirement in Method 2). One should never do this (i.e. allow the Unix passwords to be sniffed on the network).

Regarding reverse connections (e.g. -R connect:host

and -connect host), when the -localhost constraint is in effect then reverse connections can only be used to connect to the same machine x11vnc is running on (default port 5500). Please use a ssh or stunnel port redirection to the viewer machine to tunnel the reverse connection over an encrypted channel.

In -inetd mode the Method 1) will be enforced (not

Method 2). With -ssl in effect reverse connections are disabled. If you override this via env. var, be sure to also use encryption from the viewer to inetd. Tip: you can also have your own stunnel spawn x11vnc in -inetd mode (thereby bypassing inetd). See the FAQ for details.

The user names in the comma separated [list] can have

per-user options after a ":", e.g. "fred:opts" where "opts" is a "+" separated list of "viewonly", "fullaccess", "input=XXXX", or "deny", e.g. "karl,wally:viewonly,boss:input=M". For "input=" it is the K,M,B,C described under -input.

If an item in the list is "*" that means those

options apply to all users. It also means all users are allowed to log in after supplying a valid password. Use "deny" to explicitly deny some users if you use "*" to set a global option. If [list] begins with the "!" character then "*" is ignored for checking if the user is allowed, but the any value of options associated with it does apply as normal.

There are also some utilities for testing password

if [list] starts with the "%" character. See the quick_pw() function in the source for details.

-unixpw_nis [list]

As -unixpw above, however do not use

su(1) but rather use the traditional getpwnam(3) + crypt(3) method to verify passwords. All of the above -unixpw options and contraints apply.

This mode requires that the encrypted passwords be

readable. Encrypted passwords stored in /etc/shadow will be inaccessible unless x11vnc is run as root.

This is called "NIS" mode simply because in most

NIS setups user encrypted passwords are accessible (e.g. "ypcat passwd") by an ordinary user and so that user can authenticate ANY user.

NIS is not required for this mode to work (only that

getpwnam(3) return the encrypted password is required), but it is unlikely it will work for any most modern environments unless x11vnc is run as root to be able to access /etc/shadow (note running as root is often done when running x11vnc from inetd and xdm/gdm/kdm).

Looked at another way, if you do not want to use the

su(1) method provided by -unixpw, you can run x11vnc as root and use -unixpw_nis. Any users with passwords in /etc/shadow can then be authenticated. You may want to use -users unixpw= to switch the process user after the user logs in.

-unixpw_cmd cmd

As -unixpw above, however do not use

su(1) but rather run the externally supplied command cmd. The first line of its stdin will the username and the second line the received password. If the command exits with status 0 (success) the VNC client will be accepted. It will be rejected for any other return status.

Dynamic passwords and non-unix passwords can be

implemented this way by providing your own custom helper program. Note that under unixpw mode the remote viewer is given 3 tries to enter the correct password.

If a list of allowed users is needed use -unixpw [list]

in addition to this option.

-find

Find the user's display using FINDDISPLAY. This is an

alias for "-display WAIT:cmd=FINDDISPLAY".

For this and the next few options see -display WAIT:...

below for all of the details.

-finddpy

Run the FINDDISPLAY program, print out the found

display (if any) and exit. Output is like: DISPLAY=:0.0 DISPLAY=:0.0,XPID=12345 or DISPLAY=:0.0,VT=7. XPID is the process ID of the found X server. VT is the Linux virtual terminal of the X server.

-listdpy

Have the FINDDISPLAY program list all of your displays

(i.e. all the X displays on the local machine that you have access rights to).

-create

First try to find the user's display using FINDDISPLAY,

if that doesn't succeed create an X session via the FINDCREATEDISPLAY method. This is an alias for "-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb".

SSH NOTE: for both -find and -create you can (should!)

add the "-localhost" option to force SSH tunnel access.

-xdummy

As in -create, except Xdummy instead of Xvfb.

-xvnc

As in -create, except Xvnc instead of Xvfb.

-xvnc_redirect

As in -create, except Xvnc.redirect instead of Xvfb.

-svc

Terminal services mode based on SSL access. Alias for

-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users unixpw= -ssl SAVE Also "-service".

-svc_xdummy

As -svc except Xdummy instead of Xvfb.

-svc_xvnc

As -svc except Xvnc instead of Xvfb.

-xdmsvc

Display manager Terminal services mode based on SSL.

Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp -unixpw -users unixpw= -ssl SAVE Also "-xdm_service".

To create a session a user will have to first log in

to the -unixpw dialog and then log in again to the XDM/GDM/KDM prompt. Subsequent re-connections will only require the -unixpw password. See the discussion under -display WAIT:... for more details about XDM, etc configuration.

-sshxdmsvc

Display manager Terminal services mode based on SSH.

Alias for -display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp -localhost.

The -localhost option constrains connections to come

in via a SSH tunnel (which will require a login). To create a session a user will also have to log into the XDM GDM KDM prompt. Subsequent re-connections will only only require the SSH login. See the discussion under -display WAIT:... for more details about XDM, etc configuration.

-redirect port

As in FINDCREATEDISPLAY-Xvnc.redirect mode except

redirect immediately (i.e. without X session finding or creation) to a VNC server listening on port. You can also supply host:port to redirect to a different machine.

If 0 <= port < 200 it is taken as a VNC display (5900 is

added to get the actual port), if port < 0 then -port is used.

Probably the only reason to use the -redirect option is

in conjunction with SSL support, e.g. -ssl, -ssl SAVE. This provides an easy way to add SSL encryption to a VNC server that does not support SSL (e.g. Xvnc or vnc.so) In fact, the protocol does not even need to be VNC, and so "-ssl SAVE -redirect host:port" can act as a replacement for stunnel(1).

-display WAIT:...

A special usage mode for the normal -display option.

Useful with -unixpw, but can be used independently of it. If the display string begins with WAIT: then x11vnc waits until a VNC client connects before opening the X display (or -rawfb device).

This could be useful for delaying opening the display

for certain usage modes (say if x11vnc is started at boot time and no X server is running or users logged in yet).

If the string is, e.g. WAIT:0.0 or WAIT:1, i.e. "WAIT"

in front of a normal X display, then that indicated display is used.

One can also insert a geometry between colons, e.g.

WAIT:1280x1024:... to set the size of the display the VNC client first attaches to since some VNC viewers will not automatically adjust to a new framebuffer size.

A more interesting case is like this:

WAIT:cmd=/usr/local/bin/find_display

in which case the command after "cmd=" is run to

dynamically work out the DISPLAY and optionally the XAUTHORITY data. The first line of the command output must be of the form DISPLAY=<xdisplay>. On Linux if the virtual terminal is known append ",VT=n" to this string and the chvt(1) program will also be run. Any remaining output is taken as XAUTHORITY data. It can be either of the form XAUTHORITY=<file> or raw xauthority data for the display (e.g. "xauth extract - $DISPLAY" output).

In the case of -unixpw (but not -unixpw_nis), then the

above command is run as the user who just authenticated via the login and password prompt.

Also in the case of -unixpw, the user logging in can

place a colon at the end of her username and supply a few options: scale=, scale_cursor= (or sc=), solid (or so), id=, clear_mods (or cm), clear_keys (or ck), repeat, speeds= (or sp=), readtimeout= (or rd=), rotate= (or ro=), or noncache (or nc) separated by commas if there is more than one. After the user logs in successfully, these options will be applied to the VNC screen. For example,

login: fred:scale=3/4,sc=1,repeat

Password: ...

login: runge:sp=modem,rd=120,solid

for convenience m/n implies scale= e.g. fred:3/4 If you

type and enter your password incorrectly, to retrieve your long "login:" line press the Up arrow once (before typing anything else).

Another option is "geom=WxH" or "geom=WxHxD" (or

ge=). This only has an effect in FINDCREATEDISPLAY mode when a virtual X server such as Xvfb is going to be created. It sets the width and height of the new display, and optionally the color depth as well. You can also supply "gnome", "kde", "twm", "fvwm", "mwm", "dtwm", "wmaker", "xfce", "enlightenment", "Xsession", or "failsafe" (same as "xterm") to have the created display use that mode for the user session.

To disable the option setting set the environment

variable X11VNC_NO_UNIXPW_OPTS=1 before starting x11vnc. To set any other options, the user can use the gui (x11vnc -gui connect) or the remote control method (x11vnc -R opt:val) during his VNC session.

The combination of -display WAIT:cmd=... and -unixpw

allows automatic pairing of an unix authenticated VNC user with his desktop. This could be very useful on SunRays and also any system where multiple users share a given machine. The user does not need to remember special ports or passwords set up for his desktop and VNC.

A nice way to use WAIT:cmd=... is out of

inetd(8) (it automatically forks a new x11vnc for each user). You can have the x11vnc inetd spawned process run as, say, root or nobody. When run as root (for either inetd or display manager), you can also supply the option "-users unixpw=" to have the x11vnc process switch to the user as well. Note: there will be a 2nd SSL helper process that will not switch, but it is only encoding and decoding the encrypted stream at that point.

As a special case, WAIT:cmd=FINDDISPLAY will run a

script that works on most Unixes to determine a user's DISPLAY variable and xauthority data (see who(1) ).

To have this default script printed to stdout (e.g. for

customization) run with WAIT:cmd=FINDDISPLAY-print To have the script run to print what display it would find use "-finddpy" or WAIT:cmd=FINDDISPLAY-run

As another special case, WAIT:cmd=HTTPONCE will allow

x11vnc to service one http request and then exit. This is usually done in -inetd mode to run on, say, port 5800 and allow the Java vncviewer to be downloaded by client web browsers. For example:

5815 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc \

-inetd -q -http_ssl -prog /.../x11vnc \ -display WAIT:cmd=HTTPONCE

Where /.../x11vnc is the full path to x11vnc.

It is used in the Apache SSL-portal example (see FAQ).

In this mode you can set X11VNC_SKIP_DISPLAY to a comma

separated list of displays (e.g. ":0,:1") to ignore in the finding process. This can also be set by the user via "nd=" using "-" instead of ","

An interesting option is WAIT:cmd=FINDCREATEDISPLAY

that is like FINDDISPLAY in that is uses the same method to find an existing display. However, if it does not find one it will try to *start* up an X server session for the user. This is the only time x11vnc tries to actually start up an X server.

By default FINDCREATEDISPLAY will try Xdummy and then

Xvfb:

The Xdummy wrapper is part of the x11vnc source code

(x11vnc/misc/Xdummy) It should be available in PATH and have run "Xdummy -install" once to create the shared library. Xdummy requires root permission and only works on Linux. (Note: specify FD_XDUMMY_NOROOT=1 to skip a check for the root id; evidently your sudo(1) will take care of everything. The -xdummy and -svc_xdummy options imply FD_XDUMMY_NOROOT=1).

Xvfb is available on most platforms and does not

require root.

When x11vnc exits (i.e. user disconnects) the X

server session stays running in the background. The FINDDISPLAY will find it directly next time. The user must exit the X session in the usual way for it to terminate (or kill the X server process if all else fails).

So this is a somewhat odd mode for x11vnc in that it

will start up and poll virtual X servers! This can be used from, say, inetd(8) to provide a means of definitely getting a desktop (either real or virtual) on the machine. E.g. a desktop service:

5900 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc

-inetd -q -http -ssl SAVE -unixpw -users unixpw=\ -passwd secret -prog /.../x11vnc \ -display WAIT:cmd=FINDCREATEDISPLAY

Where /.../x11vnc is the full path to x11vnc.

If for some reason you do not want x11vnc to ever

try to find an existing display set the env. var X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (also -env ...)

Use WAIT:cmd=FINDCREATEDISPLAY-print to print out the

script used.

You can specify the preferred X server order via e.g.,

WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb,X and/or leave out ones you do not want. The the case "X" means try to start up a real, hardware X server using xinit(1) or startx(1). If there is already an X server running the X case may only work on Linux (see startx(1) ).

"Xvnc" will start up a VNC X server (real-

or tight-vnc, e.g. use if Xvfb is not available). "Xsrv" will start up the server program in the variable "FD_XSRV" if it is non-empty. You can make this be a wrapper script if you like (it must handle :N, -geometry, and -depth and other X server options).

You can set the environment variable FD_GEOM (or

X11VNC_CREATE_GEOM) to WxH or WxHxD to set the width and height and optionally the color depth of the created display. You can also set FD_SESS to be the session (short name of the windowmanager: kde, gnome, twm, failsafe, etc.). FD_OPTS as extra options to pass to the X server. You can also set FD_PROG to be the full path to the session/windowmanager program.

More FD tricks: FD_CUPS=port or FD_CUPS=host:port

will set the cups printing environment. Similarly for FD_ESD=port or FD_ESD=host:port for esddsp sound redirection. FD_XDUMMY_NOROOT means the Xdummy server does not need to be started as root (e.g. it will sudo automatically)

If you want the FINDCREATEDISPLAY session to contact an

XDMCP login manager (xdm/gdm/kdm) on the same machine, then use "Xvfb.xdmcp" instead of "Xvfb", etc. The user will have to supply his username and password one more time (but he gets to select his desktop type so that can be useful). For this to work, you will need to enable localhost XDMCP (udp port 177) for the display manager. This seems to be:

for gdm in gdm.conf: Enable=true in section [xdmcp]

for kdm in kdmrc: Enable=true in section [Xdmcp] for xdm in xdm-config: DisplayManager.requestPort: 177

See the shorthand options above "-svc", "-xdmsvc"

and "-sshxdmsvc" that specify the above options for some useful cases.

If you set the env. var WAITBG=1 x11vnc will go into

the background once listening in wait mode.

Another special mode is FINDCREATEDISPLAY-Xvnc.redirect,

(or FINDDISPLAY-Xvnc.redirect). In this case it will start up Xvnc as above if needed, but instead of polling it in its normal way, it simply does a socket redirection of the connected VNC viewer to the Xvnc.

So in Xvnc.redirect x11vnc does no VNC but merely

transfers the data back and forth. This should be faster then x11vnc's polling method, but not as fast as connecting directly to the Xvnc with the VNC Viewer. The idea here is to take advantage of x11vnc's display finding/creating scheme, SSL, and perhaps a few others. Most of x11vnc's options do not apply in this mode.

Xvnc.redirect should also work for the vnc.so X server

module for the h/w display however it will work only for finding the display and the user must already be logged into the X console.

-nossl

Disable the -ssl option (see below). Since -ssl is off

by default -nossl would only be used on the commandline to unset any *earlier* -ssl option (or -svc...)

-ssl [pem]

Use the openssl library (www.openssl.org) to provide a

built-in encrypted SSL tunnel between VNC viewers and x11vnc. This requires libssl support to be compiled into x11vnc at build time. If x11vnc is not built with libssl support it will exit immediately when -ssl is prescribed.

[pem] is optional, use "-ssl /path/to/mycert.pem"

to specify a PEM certificate file to use to identify and provide a key for this server. See openssl(1) for more info about PEMs and the -sslGenCert option below.

The connecting VNC viewer SSL tunnel can optionally

authenticate this server if they have the public key part of the certificate (or a common certificate authority, CA, is a more sophisicated way to verify this server's cert, see -sslGenCA below). This is used to prevent man-in-the-middle attacks. Otherwise, if the VNC viewer accepts this server's key without verification, at least the traffic is protected from passive sniffing on the network (but NOT from man-in-the-middle attacks).

If [pem] is not supplied and the

openssl(1) utility command exists in PATH, then a temporary, self-signed certificate will be generated for this session (this may take 5-30 seconds on slow machines). If openssl(1) cannot be used to generate a temporary certificate x11vnc exits immediately.

If successful in using

openssl(1) to generate a temporary certificate, the public part of it will be displayed to stderr (e.g. one could copy it to the client-side to provide authentication of the server to VNC viewers.) See following paragraphs for how to save keys to reuse when x11vnc is restarted.

Set the env. var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc

print out the entire certificate, including the PRIVATE KEY part, to stderr. One could reuse this cert if saved in a [pem] file. Similarly, set X11VNC_KEEP_TMP_PEM=1 to not delete the temporary PEM file: the file name will be printed to stderr (so one could move it to a safe place for reuse). You will be prompted for a passphrase for the private key.

If [pem] is "SAVE" then the certificate will be saved

to the file ~/.vnc/certs/server.pem, or if that file exists it will be used directly. Similarly, if [pem] is "SAVE_PROMPT" the server.pem certificate will be made based on your answers to its prompts for info such as OrganizationalName, CommonName, etc.

Use "SAVE-<string>" and "SAVE_PROMPT-<string>"

to refer to the file ~/.vnc/certs/server-<string>.pem instead. E.g. "SAVE-charlie" will store to the file ~/.vnc/certs/server-charlie.pem

See -ssldir below to use a directory besides the

default ~/.vnc/certs

Example: x11vnc -ssl SAVE -display :0 ...

Your VNC viewer will also need to be able to connect

via SSL. See the discussion below under -stunnel and the FAQ (ss_vncviewer script) for how this might be achieved. E.g. on Unix it is easy to write a shell script that starts up stunnel and then vncviewer. Also in the x11vnc source a SSL enabled Java VNC Viewer applet is provided in the classes/ssl directory.

-ssltimeout n

Set SSL read timeout to n seconds. In some situations

(i.e. an iconified viewer in Windows) the viewer stops talking and the connection is dropped after the default timeout (25s for about the first minute, 43200s later). Set to zero to poll forever. Set to a negative value to use the builtin setting.

-sslnofail

Exit at the first SSL connection failure. Useful when

scripting SSL connections (e.g. x11vnc is started via ssh) and you do not want x11vnc waiting around for more connections, tying up ports, etc.

-ssldir [dir]

Use [dir] as an alternate ssl certificate and key

management toplevel directory. The default is ~/.vnc/certs

This directory is used to store server and other

certificates and keys and also other materials. E.g. in the simplest case, "-ssl SAVE" will store the x11vnc server cert in [dir]/server.pem

Use of alternate directories via -ssldir allows you to

manage multiple VNC Certificate Authority (CA) keys. Another use is if ~/.vnc/cert is on an NFS share you might want your certificates and keys to be on a local filesystem to prevent network snooping (for example -ssldir /var/lib/x11vnc-certs).

-ssldir affects nearly all of the other -ssl* options,

e.g. -ssl SAVE, -sslGenCert, etc..

-sslverify [path]

For either of the -ssl or -stunnel modes, use [path]

to provide certificates to authenticate incoming VNC *Client* connections (normally only the server is authenticated in SSL.) This can be used as a method to replace standard password authentication of clients.

If [path] is a directory it contains the client (or CA)

certificates in separate files. If [path] is a file, it contains multiple certificates. See special tokens below. These correspond to the "CApath = dir" and "CAfile = file" stunnel options. See the stunnel(8) manpage for details.

Examples:

x11vnc -ssl -sslverify ~/my.crt x11vnc -ssl -sslverify ~/my_pem_dir/

Note that if [path] is a directory, it must contain

the certs in separate files named like <HASH>.0, where the value of <HASH> is found by running the command "openssl x509 -hash -noout -in file.crt". Evidently one uses <HASH>.1 if there is a collision...

The the key-management utility "-sslCertInfo HASHON"

and "-sslCertInfo HASHOFF" will create/delete these hashes for you automatically (via symlink) in the HASH subdirs it manages. Then you can point -sslverify to the HASH subdir.

Special tokens: in -ssl mode, if [path] is not a file or

a directory, it is taken as a comma separated list of tokens that are interpreted as follows:

If a token is "CA" that means load the CA/cacert.pem

file from the ssl directory. If a token is "clients" then all the files clients/*.crt in the ssl directory are loaded. Otherwise the file clients/token.crt is attempted to be loaded. As a kludge, use a token like ../server-foo to load a server cert if you find that necessary.

Use -ssldir to use a directory different from the

~/.vnc/certs default.

Note that if the "CA" cert is loaded you do not need

to load any of the certs that have been signed by it. You will need to load any additional self-signed certs however.

Examples:

x11vnc -ssl -sslverify CA x11vnc -ssl -sslverify self:fred,self:jim x11vnc -ssl -sslverify CA,clients

Usually "-sslverify CA" is the most effective.

See the -sslGenCA and -sslGenCert options below for how to set up and manage the CA framework.

NOTE: the following utilities, -sslGenCA, -sslGenCert,

-sslEncKey, and -sslCertInfo are provided for completeness, but for casual usage they are overkill.

They provide VNC Certificate Authority (CA) key creation

and server / client key generation and signing. So they provide a basic Public Key management framework for VNC-ing with x11vnc. (note that they require openssl(1) be installed on the system)

However, the simplest usage mode (where x11vnc

automatically generates its own, self-signed, temporary key and the VNC viewers always accept it, e.g. accepting via a dialog box) is probably safe enough for most scenarios. CA management is not needed.

To protect against Man-In-The-Middle attacks the

simplest mode can be improved by using "-ssl SAVE" to have x11vnc create a longer term self-signed certificate, and then (safely) copy the corresponding public key cert to the desired client machines (care must be taken the private key part is not stolen; you will be prompted for a passphrase).

So keep in mind no CA key creation or management

(-sslGenCA and -sslGenCert) is needed for either of the above two common usage modes.

One might want to use -sslGenCA and -sslGenCert

if you had a large number of VNC client and server workstations. That way the administrator could generate a single CA key with -sslGenCA and distribute its certificate part to all of the workstations.

Next, he could create signed VNC server keys

(-sslGenCert server ...) for each workstation or user that then x11vnc would use to authenticate itself to any VNC client that has the CA cert.

Optionally, the admin could also make it so the

VNC clients themselves are authenticated to x11vnc (-sslGenCert client ...) For this -sslverify would be pointed to the CA cert (and/or self-signed certs).

x11vnc will be able to use all of these cert and

key files. On the VNC client side, they will need to be "imported" somehow. Web browsers have "Manage Certificates" actions as does the Java applet plugin Control Panel. stunnel can also use these files (see the ss_vncviewer example script in the FAQ.)

-sslGenCA [dir]

Generate your own Certificate Authority private key,

certificate, and other files in directory [dir].

If [dir] is not supplied, a -ssldir setting is used,

or otherwise ~/.vnc/certs is used.

This command also creates directories where server and

client certs and keys will be stored. The openssl(1) program must be installed on the system and available in PATH.

After the CA files and directories are created the

command exits; the VNC server is not run.

You will be prompted for information to put into the CA

certificate. The info does not have to be accurate just as long as clients accept the cert for VNC connections. You will also need to supply a passphrase of at least 4 characters for the CA private key.

Once you have generated the CA you can distribute

its certificate part, [dir]/CA/cacert.pem, to other workstations where VNC viewers will be run. One will need to "import" this certicate in the applications, e.g. Web browser, Java applet plugin, stunnel, etc. Next, you can create and sign keys using the CA with the -sslGenCert option below.

Examples:

x11vnc -sslGenCA x11vnc -sslGenCA ~/myCAdir x11vnc -ssldir ~/myCAdir -sslGenCA

(the last two lines are equivalent)

-sslGenCert type name

Generate a VNC server or client certificate and private

key pair signed by the CA created previously with -sslGenCA. The openssl(1) program must be installed on the system and available in PATH.

After the Certificate is generated the command exits;

the VNC server is not run.

The type of key to be generated is the string type.

It is either "server" (i.e. for use by x11vnc) or "client" (for a VNC viewer). Note that typically only "server" is used: the VNC clients authenticate themselves by a non-public-key method (e.g. VNC or unix password). type is required.

An arbitrary default name you want to associate with

the key is supplied by the name string. You can change it at the various prompts when creating the key. name is optional.

If name is left blank for clients keys then "nobody"

is used. If left blank for server keys, then the primary server key: "server.pem" is created (this is the saved one referenced by "-ssl SAVE" when the server is started)

If name begins with the string "self:" then

a self-signed certificate is created instead of one signed by your CA key.

If name begins with the string "req:" then only a

key (.key) and a certificate signing *request* (.req) are generated. You can then send the .req file to an external CA (even a professional one, e.g. Thawte) and then combine the .key and the received cert into the .pem file with the same basename.

The distinction between "server" and "client" is

simply the choice of output filenames and sub-directory. This makes it so the -ssl SAVE-name option can easily pick up the x11vnc PEM file this option generates. And similarly makes it easy for the -sslverify option to pick up your client certs.

There is nothing special about the filename or directory

location of either the "server" and "client" certs. You can rename the files or move them to wherever you like.

Precede this option with -ssldir [dir] to use a

directory other than the default ~/.vnc/certs You will need to run -sslGenCA on that directory first before doing any -sslGenCert key creation.

Note you cannot recreate a cert with exactly the same

distiguished name (DN) as an existing one. To do so, you will need to edit the [dir]/CA/index.txt file to delete the line.

Similar to -sslGenCA, you will be prompted to fill

in some information that will be recorded in the certificate when it is created. Tip: if you know the fully-quailified hostname other people will be connecting to you can use that as the CommonName "CN" to avoid some applications (e.g. web browsers and java plugin) complaining it does not match the hostname.

You will also need to supply the CA private key

passphrase to unlock the private key created from -sslGenCA. This private key is used to sign the server or client certicate.

The "server" certs can be used by x11vnc directly by

pointing to them via the -ssl [pem] option. The default file will be ~/.vnc/certs/server.pem. This one would be used by simply typing -ssl SAVE. The pem file contains both the certificate and the private key. server.crt file contains the cert only.

The "client" cert + private key file will need

to be copied and imported into the VNC viewer side applications (Web browser, Java plugin, stunnel, etc.) Once that is done you can delete the "client" private key file on this machine since it is only needed on the VNC viewer side. The, e.g. ~/.vnc/certs/clients/<name>.pem contains both the cert and private key. The <name>.crt contains the certificate only.

NOTE: It is very important to know one should always

generate new keys with a passphrase. Otherwise if an untrusted user steals the key file he could use it to masquerade as the x11vnc server (or VNC viewer client). You will be prompted whether to encrypt the key with a passphrase or not. It is recommended that you do. One inconvenience to a passphrase is that it must be suppled every time x11vnc or the client app is started up.

Examples:

x11vnc -sslGenCert server

x11vnc -ssl SAVE -display :0 ...

and then on viewer using ss_vncviewer stunnel wrapper

(see the FAQ): ss_vncviewer -verify ./cacert.crt hostname:0

(this assumes the cacert.crt cert from -sslGenCA

was safely copied to the VNC viewer machine where ss_vncviewer is run)

Example using a name:

x11vnc -sslGenCert server charlie

x11vnc -ssl SAVE-charlie -display :0 ...

Example for a client certificate (rarely used):

x11vnc -sslGenCert client roger

scp ~/.vnc/certs/clients/roger.pem somehost:. rm ~/.vnc/certs/clients/roger.pem

x11vnc is then started with the the option -sslverify

~/.vnc/certs/clients/roger.crt (or simply -sslverify roger), and on the viewer user on somehost could do for example:

ss_vncviewer -mycert ./roger.pem hostname:0

If you set the env. var REQ_ARGS='...' it will be

passed to openssl req(1). A common use would be REQ_ARGS='-days 730' to bump up the expiration date (2 years in this case).

-sslEncKey [pem]

Utility to encrypt an existing PEM file with a

passphrase you supply when prompted. For that key to be used (e.g. by x11vnc) the passphrase must be supplied each time.

The "SAVE" notation described under -ssl applies as

well. (precede this option with -ssldir [dir] to refer a directory besides the default ~/.vnc/certs)

The

openssl(1) program must be installed on the system and available in PATH. After the Key file is encrypted the command exits; the VNC server is not run.

Examples:

x11vnc -sslEncKey /path/to/foo.pem x11vnc -sslEncKey SAVE x11vnc -sslEncKey SAVE-charlie

-sslCertInfo [pem]

Prints out information about an existing PEM file.

In addition the public certificate is also printed. The openssl(1) program must be in PATH. Basically the command "openssl x509 -text" is run on the pem.

The "SAVE" notation described under -ssl applies

as well.

Using "LIST" will give a list of all certs being

managed (in the ~/.vnc/certs dir, use -ssldir to refer to another dir). "ALL" will print out the info for every managed key (this can be very long). Giving a client or server cert shortname will also try a lookup (e.g. -sslCertInfo charlie). Use "LISTL" or "LL" for a long (ls -l style) listing.

Using "HASHON" will create subdirs [dir]/HASH and

[dir]/HASH with OpenSSL hash filenames (e.g. 0d5fbbf1.0) symlinks pointing up to the corresponding *.crt file. ([dir] is ~/.vnc/certs or one given by -ssldir.) This is a useful way for other OpenSSL applications (e.g. stunnel) to access all of the certs without having to concatenate them. x11vnc will not use them unless you specifically reference them. "HASHOFF" removes these HASH subdirs.

The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can

also be lowercase, e.g. "list".

-sslDelCert [pem]

Prompts you to delete all .crt .pem .key .req files

associated with [pem]. "SAVE" and lookups as in -sslCertInfo apply as well.

-stunnel [pem]

Use the

stunnel(8) (www.stunnel.org) to provide an encrypted SSL tunnel between viewers and x11vnc.

This external tunnel method was implemented prior to the

integrated -ssl encryption described above. It still works well. This requires stunnel to be installed on the system and available via PATH (n.b. stunnel is often installed in sbin directories). Version 4.x of stunnel is assumed (but see -stunnel3 below.)

[pem] is optional, use "-stunnel /path/to/stunnel.pem"

to specify a PEM certificate file to pass to stunnel. Whether one is needed or not depends on your stunnel configuration. stunnel often generates one at install time. See the stunnel documentation for details.

stunnel is started up as a child process of x11vnc and

any SSL connections stunnel receives are decrypted and sent to x11vnc over a local socket. The strings "The SSL VNC desktop is ..." and "SSLPORT=..." are printed out at startup to indicate this.

The -localhost option is enforced by default

to avoid people routing around the SSL channel. Set STUNNEL_DISABLE_LOCALHOST=1 before starting x11vnc to disable the requirement.

Your VNC viewer will also need to be able to connect via

SSL. Unfortunately not too many do this. UltraVNC has an encryption plugin but it does not seem to be SSL.

Also, in the x11vnc distribution, a patched TightVNC

Java applet is provided in classes/ssl that does SSL connections (only).

It is also not too difficult to set up an stunnel or

other SSL tunnel on the viewer side. A simple example on Unix using stunnel 3.x is:

% stunnel -c -d localhost:5901 -r remotehost:5900

% vncviewer localhost:1

For Windows, stunnel has been ported to it and there

are probably other such tools available. See the FAQ for more examples.

-stunnel3 [pem]

Use version 3.x stunnel command line syntax instead of

version 4.x

-https [port]

Choose a separate HTTPS port (-ssl mode only).

In -ssl mode, it turns out you can use the

single VNC port (e.g. 5900) for both VNC and HTTPS connections. (HTTPS is used to retrieve a SSL-aware VncViewer.jar applet that is provided with x11vnc). Since both use SSL the implementation was extended to detect if HTTP traffic (i.e. GET) is taking place and handle it accordingly. The URL would be, e.g.:

https://mymachine.org:5900/

This is convenient for firewalls, etc, because only one

port needs to be allowed in. However, this heuristic adds a few seconds delay to each connection and can be unreliable (especially if the user takes much time to ponder the Certificate dialogs in his browser, Java VM, or VNC Viewer applet. That's right 3 separate "Are you sure you want to connect?" dialogs!)

So use the -https option to provide a separate, more

reliable HTTPS port that x11vnc will listen on. If [port] is not provided (or is 0), one is autoselected. The URL to use is printed out at startup.

The SSL Java applet directory is specified via the

-httpdir option. If not supplied it will try to guess the directory as though the -http option was supplied.

-httpsredir [port]

In -ssl mode with the Java applet retrieved via HTTPS,

when the HTML file containing applet parameters ('index.vnc' or 'proxy.vnc') is sent do NOT set the applet PORT parameter to the actual VNC port but set it to "port" instead. If "port" is not supplied, then the port number is guessed from the Host: HTTP header.

This is useful when an incoming TCP connection

redirection is performed by a router/gateway/firewall from one port to an internal machine where x11vnc is listening on a different port. The Java applet needs to connect to the firewall/router port, not the VNC port on the internal workstation. For example, one could redir from mygateway.com:443 to workstation:5900.

This spares the user from having to type in

https://mygateway.com/?PORT=443 into their web browser. Note taht port 443 is the default https port; other ports must be explicity indicated, for example: https://mygateway.com:8000/?PORT=8000. To avoid having to include the PORT= in the browser URL, simply supply "-httpsredir" to x11vnc.

-usepw

If no other password method was supplied on the command

line, first look for ~/.vnc/passwd and if found use it with -rfbauth; next, look for ~/.vnc/passwdfile and use it with -passwdfile; otherwise, prompt the user for a password to create ~/.vnc/passwd and use it with the -rfbauth option. If none of these succeed x11vnc exits immediately.

-storepasswd pass file

Store password pass as the VNC password in the

file file. Once the password is stored the program exits. Use the password via "-rfbauth file"

If called with no arguments, "x11vnc -storepasswd",

the user is prompted for a password and it is stored in the file ~/.vnc/passwd. Called with one argument, that will be the file to store the prompted password in.

-nopw

Disable the big warning message when you use x11vnc

without some sort of password.

-accept string

Run a command (possibly to prompt the user at the

X11 display) to decide whether an incoming client should be allowed to connect or not. string is an external command run via system(3) or some special cases described below. Be sure to quote string if it contains spaces, shell characters, etc. If the external command returns 0 the client is accepted, otherwise the client is rejected. See below for an extension to accept a client view-only.

If x11vnc is running as root (say from

inetd(8) or from display managers xdm(1) , gdm(1) , etc), think about the security implications carefully before supplying this option (likewise for the -gone option).

Environment: The RFB_CLIENT_IP environment variable will

be set to the incoming client IP number and the port in RFB_CLIENT_PORT (or -1 if unavailable). Similarly, RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side of the connection), are set to allow identification of the tcp virtual circuit. The x11vnc process id will be in RFB_X11VNC_PID, a client id number in RFB_CLIENT_ID, and the number of other connected clients in RFB_CLIENT_COUNT. RFB_MODE will be "accept". RFB_STATE will be PROTOCOL_VERSION, SECURITY_TYPE, AUTHENTICATION, INITIALISATION, NORMAL, or UNKNOWN indicating up to which state the client has acheived. RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown). RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may also be set.

If string is "popup" then a builtin popup window

is used. The popup will time out after 120 seconds, use "popup:N" to modify the timeout to N seconds (use 0 for no timeout).

In the case of "popup" and when the -unixpw option

is specified, then a *second* window will be popped up after the user successfully logs in via his UNIX password. This time the user will be identified as UNIX:username@hostname, the "UNIX:" prefix indicates which user the viewer logged as via -unixpw. The first popup is only for whether to allow him to even *try* to login via unix password.

If string is "xmessage" then an

xmessage(1) invocation is used for the command. xmessage must be installed on the machine for this to work.

Both "popup" and "xmessage" will present an option

for accepting the client "View-Only" (the client can only watch). This option will not be presented if -viewonly has been specified, in which case the entire display is view only.

If the user supplied command is prefixed with something

like "yes:0,no:*,view:3 mycommand ..." then this associates the numerical command return code with the actions: accept, reject, and accept-view-only, respectively. Use "*" instead of a number to indicate the default action (in case the command returns an unexpected value). E.g. "no:*" is a good choice.

Note that x11vnc blocks while the external command

or popup is running (other clients may see no updates during this period). So a person sitting a the physical display is needed to respond to an popup prompt. (use a 2nd x11vnc if you lock yourself out).

More -accept tricks: use "popupmouse" to only allow

mouse clicks in the builtin popup to be recognized. Similarly use "popupkey" to only recognize keystroke responses. These are to help avoid the user accidentally accepting a client by typing or clicking. All 3 of the popup keywords can be followed by +N+M to supply a position for the popup window. The default is to center the popup window.

-afteraccept string

As -accept, except to run a user supplied command after

a client has been accepted and authenticated. RFB_MODE will be set to "afteraccept" and the other RFB_* variables are as in -accept. Unlike -accept, the command return code is not interpreted by x11vnc. Example: -afteraccept 'killall xlock &'

-gone string

As -accept, except to run a user supplied command when

a client goes away (disconnects). RFB_MODE will be set to "gone" and the other RFB_* variables are as in -accept. The "popup" actions apply as well. Unlike -accept, the command return code is not interpreted by x11vnc. Example: -gone 'xlock &'

-users list

If x11vnc is started as root (say from

inetd(8) or from display managers xdm(1) , gdm(1) , etc), then as soon as possible after connections to the X display are established try to switch to one of the users in the comma separated list. If x11vnc is not running as root this option is ignored.

Why use this option? In general it is not needed since

x11vnc is already connected to the X display and can perform its primary functions. The option was added to make some of the *external* utility commands x11vnc occasionally runs work properly. In particular under GNOME and KDE to implement the "-solid color" feature external commands (gconftool-2 and dcop) unfortunately must be run as the user owning the desktop session. Since this option switches userid it also affects the userid used to run the processes for the -accept and -gone options. It also affects the ability to read files for options such as -connect, -allow, and -remap and also the ultra and tight filetransfer feature if enabled. Note that the -connect file is also sometimes written to.

So be careful with this option since in some situations

its use can decrease security.

In general the switch to a user will only take place

if the display can still be successfully opened as that user (this is primarily to try to guess the actual owner of the session). Example: "-users fred,wilma,betty". Note that a malicious local user "barney" by quickly using "xhost +" when logging in may possibly get the x11vnc process to switch to user "fred". What happens next?

Under display managers it may be a long time before

the switch succeeds (i.e. a user logs in). To instead make it switch immediately regardless if the display can be reopened prefix the username with the "+" character. E.g. "-users +bob" or "-users +nobody".

The latter (i.e. switching immediately to user

"nobody") is the only obvious use of the -users option that increases security.

Use the following notation to associate a group with

a user: user1.group1,user2.group2,... Note that initgroups(2) will still be called first to try to switch to ALL of a user's groups (primary and additional groups). Only if that fails or it is not available then the single group specified as above (or the user's primary group if not specified) is switched to with setgid(2). Use -env X11VNC_SINGLE_GROUP=1 to prevent trying initgroups(2) and only switch to the single group. This sort of setting is only really needed to make the ultra or tight filetransfer permissions work properly. This format applies to any comma separated list of users, even the special "=" modes described below.

In -unixpw mode, if "-users unixpw=" is supplied

then after a user authenticates himself via the -unixpw mechanism, x11vnc will try to switch to that user as though "-users +username" had been supplied. If you want to limit which users this will be done for, provide them as a comma separated list after "unixpw=" Groups can also be specified as described above.

Similarly, in -ssl mode, if "-users sslpeer=" is

supplied then after an SSL client authenticates with his cert (the -sslverify option is required for this) x11vnc will extract a UNIX username from the "emailAddress" field (username@hostname.com) of the "Subject" of the x509 SSL cert and then try to switch to that user as though "-users +username" had been supplied. If you want to limit which users this will be done for, provide them as a comma separated list after "sslpeer=". Set the env. var X11VNC_SSLPEER_CN to use the Common Name (normally a hostname) instead of the Email field.

NOTE: for sslpeer= mode the x11vnc administrator must

take care that any client certs he adds to -sslverify have the intended UNIX username in the "emailAddress" field of the cert. Otherwise a user may be able to log in as another. This command can be of use in checking: "openssl x509 -text -in file.crt", see the "Subject:" line. Also, along with the normal RFB_* env. vars. (see -accept) passed to external cmd= commands, RFB_SSL_CLIENT_CERT will be set to the client's x509 certificate string.

The sslpeer= mode can aid finding X sessions via the

FINDDISPLAY and FINDCREATEDISPLAY mechanisms.

To immediately switch to a user *before* connections

to the X display are made or any files opened use the "=" character: "-users =bob". That user needs to be able to open the X display and any files of course.

The special user "guess=" means to examine the utmpx

database (see who(1) ) looking for a user attached to the display number (from DISPLAY or -display option) and try him/her. To limit the list of guesses, use: "-users guess=bob,betty".

Even more sinister is the special user "lurk="

that means to try to guess the DISPLAY from the utmpx login database as well. So it "lurks" waiting for anyone to log into an X session and then connects to it. Specify a list of users after the = to limit which users will be tried. To enable a different searching mode, if the first user in the list is something like ":0" or ":0-2" that indicates a range of DISPLAY numbers that will be tried (regardless of whether they are in the utmpx database) for all users that are logged in. Also see the "-display WAIT:..." functionality. Examples: "-users lurk=" and also "-users lurk=:0-1,bob,mary"

Be especially careful using the "guess=" and "lurk="

modes. They are not recommended for use on machines with untrustworthy local users.

-noshm

Do not use the MIT-SHM extension for the polling.

Remote displays can be polled this way: be careful this can use large amounts of network bandwidth. This is also of use if the local machine has a limited number of shm segments and -onetile is not sufficient.

-flipbyteorder

Sometimes needed if remotely polled host has different

endianness. Ignored unless -noshm is set.

-onetile

Do not use the new copy_tiles() framebuffer mechanism,

just use 1 shm tile for polling. Limits shm segments used to 3.

-solid [color]

To improve performance, when VNC clients are connected

try to change the desktop background to a solid color. The [color] is optional: the default color is "cyan4". For a different one specify the X color (rgb.txt name, e.g. "darkblue" or numerical "#RRGGBB").

Currently this option only works on GNOME, KDE, CDE,

and classic X (i.e. with the background image on the root window). The "gconftool-2" and "dcop" external commands are run for GNOME and KDE respectively. Other desktops won't work, e.g. Xfce (send us the corresponding commands if you find them). If x11vnc is running as root ( inetd(8) or gdm(1) ), the -users option may be needed for GNOME and KDE. If x11vnc guesses your desktop incorrectly, you can force it by prefixing color with "gnome:", "kde:", "cde:" or "root:".

-blackout string

Black out rectangles on the screen. string is a

comma separated list of WxH+X+Y type geometries for each rectangle. If one of the items on the list is the string "noptr" the mouse pointer will not be allowed to go into a blacked out region.

-xinerama, -noxinerama

If your screen is composed of multiple monitors

glued together via XINERAMA, and that screen is not a rectangle this option will try to guess the areas to black out (if your system has libXinerama). default: -xinerama

In general, we have noticed on XINERAMA displays you may

need to use the "-xwarppointer" option if the mouse pointer misbehaves and it is enabled by default. Use "-noxwarppointer" if you do not want this.

-xtrap

Use the DEC-XTRAP extension for keystroke and mouse

input insertion. For use on legacy systems, e.g. X11R5, running an incomplete or missing XTEST extension. By default DEC-XTRAP will be used if XTEST server grab control is missing, use -xtrap to do the keystroke and mouse insertion via DEC-XTRAP as well.

-xrandr [mode]

If the display supports the XRANDR (X Resize, Rotate

and Reflection) extension, and you expect XRANDR events to occur to the display while x11vnc is running, this options indicates x11vnc should try to respond to them (as opposed to simply crashing by assuming the old screen size). See the xrandr(1) manpage and run 'xrandr -q' for more info. [mode] is optional and described below.

Since watching for XRANDR events and trapping errors

increases polling overhead, only use this option if XRANDR changes are expected. For example on a rotatable screen PDA or laptop, or using a XRANDR-aware Desktop where you resize often. It is best to be viewing with a vncviewer that supports the NewFBSize encoding, since it knows how to react to screen size changes. Otherwise, libvncserver tries to do so something reasonable for viewers that cannot do this (portions of the screen may be clipped, unused, etc).

Note: the default now is to check for XRANDR events, but

do not trap every X call that may fail due to resize. If a resize event is received, the full -xrandr mode is enabled. To disable even checking for events supply: -noxrandr.

"mode" defaults to "resize", which means create a

new, resized, framebuffer and hope all viewers can cope with the change. "newfbsize" means first disconnect all viewers that do not support the NewFBSize VNC encoding, and then resize the framebuffer. "exit" means disconnect all viewer clients, and then terminate x11vnc.

-rotate string

Rotate and/or flip the framebuffer view exported by VNC.

This transformation is independent of XRANDR and is done in software in main memory and so may be slower. This mode could be useful on a handheld with portrait or landscape modes that do not correspond to the scanline order of the actual framebuffer. string can be:

x flip along x-axis

y flip along y-axis xy flip along x- and y-axes +90 rotate 90 degrees clockwise -90 rotate 90 degrees counter-clockwise +90x rotate 90 degrees CW, then flip along x +90y rotate 90 degrees CW, then flip along y

these give all possible rotations and reflections.

Aliases: same as xy: yx, +180, -180, 180

same as -90: +270, 270 same as +90: 90, (ditto for 90x, 90y)

Like -scale, this transformation is applied at the very

end of any chain of framebuffer transformations and so any options with geometries, e.g. -blackout, -clip, etc. are relative to the original X (or -rawfb) framebuffer, not the final one sent to VNC viewers.

If you do not want the cursor shape to be rotated

prefix string with "nc:", e.g. "nc:+90", "nc:xy", etc.

-padgeom WxH

Whenever a new vncviewer connects, the framebuffer is

replaced with a fake, solid black one of geometry WxH. Shortly afterwards the framebuffer is replaced with the real one. This is intended for use with vncviewers that do not support NewFBSize and one wants to make sure the initial viewer geometry will be big enough to handle all subsequent resizes (e.g. under -xrandr, -remote id:windowid, rescaling, etc.)

-o logfile

Write stderr messages to file logfile instead of

to the terminal. Same as "-logfile file". To append to the file use "-oa file" or "-logappend file".

-flag file

Write the "PORT=NNNN" (e.g. PORT=5900) string to

file in addition to stdout. This option could be useful by wrapper script to detect when x11vnc is ready.

-rc filename

Use filename instead of $HOME/.x11vncrc for rc file.

-norc

Do not process any .x11vncrc file for options.

-env VAR=VALUE

Set the environment variable 'VAR' to value 'VALUE'

at x11vnc startup. This is a convenience utility to avoid shell script wrappers, etc. to set the env. var. You may specify as many of these as needed on the command line.

-prog /path/to/x11vnc

Set the full path to the x11vnc program for cases when

it cannot be determined from argv[0] (e.g. tcpd/inetd)

-h, -help

Print this help text.

-?, -opts Only list the x11vnc options.

-V, -version

Print program version and last modification date.

-license

Print out license information. Same as -copying and

-warranty.

-dbg

Instead of exiting after cleaning up, run a simple

"debug crash shell" when fatal errors are trapped.

-q, -quiet

Be quiet by printing less informational output to

stderr.

-v, -verbose

Print out more information to stderr.

-bg

Go into the background after screen setup. Messages to

stderr are lost unless -o logfile is used. Something like this could be useful in a script:

port='ssh -t $host "x11vnc -display :0 -bg" | grep PORT'

port='echo "$port" | sed -e 's/PORT=//''

port='expr $port - 5900'

vncviewer $host:$port

-modtweak, -nomodtweak

Option -modtweak automatically tries to adjust the AltGr

and Shift modifiers for differing language keyboards between client and host. Otherwise, only a single key press/release of a Keycode is simulated (i.e. ignoring the state of the modifiers: this usually works for identical keyboards). Also useful in resolving cases where a Keysym is bound to multiple keys (e.g. "<" + ">" and "," + "<" keys). Default: -modtweak

On some HP-UX systems it is been noted that they have

an odd keymapping where a single keycode will have a keysym, e.g. "#", up to three times. You can check via "xmodmap -pk" or the -dk option. The failure is when you try to type "#" it yields "3". If you see this problem try setting the environment variable MODTWEAK_LOWEST=1 to see if it helps.

-xkb, -noxkb

When in modtweak mode, use the XKEYBOARD extension (if

the X display supports it) to do the modifier tweaking. This is powerful and should be tried if there are still keymapping problems when using -modtweak by itself. The default is to check whether some common keysyms, e.g. !, @, [, are only accessible via -xkb mode and if so then automatically enable the mode. To disable this automatic detection use -noxkb.

When -xkb mode is active you can set these env. vars.

They apply only when there is ambiguity as to which key to choose (i.e the mapping is not one-to-one). NOKEYHINTS=1: for up ascii keystrokes do not use score hints saved when the key was pressed down. NOANYDOWN=1: for up keystrokes do not resort to searching through keys that are currently pressed down. KEYSDOWN=N: remember the last N keys press down for tie-breaking when an up keystroke comes in.

-capslock

When in -modtweak (the default) or -xkb mode,

if a keysym in the range A-Z comes in check the X server to see if the Caps_Lock is set. If it is do not artificially press Shift to generate the keysym. This will enable the CapsLock key to behave correctly in some circumstances: namely *both* the VNC viewer machine and the x11vnc X server are in the CapsLock on state. If one side has CapsLock on and the other off and the keyboard is not behaving as you think it should you should correct the CapsLock states (hint: pressing CapsLock inside and outside of the viewer can help toggle them both to the correct state). However, for best results do not use this option, but rather *only* enable CapsLock on the VNC viewer side (i.e. by pressing CapsLock outside of the viewer window, also -skip_lockkeys below). Also try -nomodtweak for a possible workaround.

-skip_lockkeys

Have x11vnc ignore all Caps_Lock, Shift_Lock, Num_Lock,

Scroll_Lock keysyms received from viewers. The idea is you press Caps_Lock on the VNC Viewer side but that does not change the lock state in the x11vnc-side X server. Nevertheless your capitalized letters come in over the wire and are applied correctly to the x11vnc-side X server. Note this mode probably won't do what you want in -nomodtweak mode. Also, a kludge for KP_n digits is always done it this mode: they are mapped to regular digit keysyms. See also -capslock above.

-skip_keycodes string

Ignore the comma separated list of decimal keycodes.

Perhaps these are keycodes not on your keyboard but your X server thinks exist. Currently only applies to -xkb mode. Use this option to help x11vnc in the reverse problem it tries to solve: Keysym -> Keycode(s) when ambiguities exist (more than one Keycode per Keysym). Run 'xmodmap -pk' to see your keymapping. Example: "-skip_keycodes 94,114"

-sloppy_keys

Experimental option that tries to correct some

"sloppy" key behavior. E.g. if at the viewer you press Shift+Key but then release the Shift before Key that could give rise to extra unwanted characters (usually only between keyboards of different languages). Only use this option if you observe problems with some keystrokes.

-skip_dups, -noskip_dups

Some VNC viewers send impossible repeated key events,

e.g. key-down, key-down, key-up, key-up all for the same key, or 20 downs in a row for the same modifier key! Setting -skip_dups means to skip these duplicates and just process the first event. Note: some VNC viewers assume they can send down's without the corresponding up's and so you should not set this option for these viewers (symptom: some keys do not autorepeat) Default: -noskip_dups

-add_keysyms, -noadd_keysyms

If a Keysym is received from a VNC viewer and that

Keysym does not exist in the X server, then add the Keysym to the X server's keyboard mapping on an unused key. Added Keysyms will be removed periodically and also when x11vnc exits. Default: -add_keysyms

-clear_mods

At startup and exit clear the modifier keys by sending

KeyRelease for each one. The Lock modifiers are skipped. Used to clear the state if the display was accidentally left with any pressed down.

-clear_keys

As -clear_mods, except try to release any pressed key.

Note that this option and -clear_mods can interfere with a person typing at the physical keyboard.

-remap string

Read Keysym remappings from file named string.

Format is one pair of Keysyms per line (can be name or hex value) separated by a space. If no file named string exists, it is instead interpreted as this form: key1-key2,key3-key4,... See <X11/keysymdef.h> header file for a list of Keysym names, or use xev(1). To map a key to a button click, use the fake Keysyms "Button1", ..., etc. E.g: "-remap Super_R-Button2" (useful for pasting on a laptop)

To disable a keysym (i.e. make it so it will not be

injected), remap it to "NoSymbol" or "None".

Dead keys: "dead" (or silent, mute) keys are keys that

do not produce a character but must be followed by a 2nd keystroke. This is often used for accenting characters, e.g. to put "'" on top of "a" by pressing the dead key and then "a". Note that this interpretation is not part of core X11, it is up to the toolkit or application to decide how to react to the sequence. The X11 names for these keysyms are "dead_grave", "dead_acute", etc. However some VNC viewers send the keysyms "grave", "acute" instead thereby disabling the accenting. To work around this -remap can be used. For example "-remap grave-dead_grave,acute-dead_acute"

As a convenience, "-remap DEAD" applies these remaps:

g grave-dead_grave

a acute-dead_acute
c asciicircum-dead_circumflex
t asciitilde-dead_tilde
m macron-dead_macron
b breve-dead_breve
D abovedot-dead_abovedot
d diaeresis-dead_diaeresis
o degree-dead_abovering
A doubleacute-dead_doubleacute
r caron-dead_caron
e cedilla-dead_cedilla

If you just want a subset use the first letter

label, e.g. "-remap DEAD=ga" to get the first two. Additional remaps may also be supplied via commas, e.g. "-remap DEAD=ga,Super_R-Button2". Finally, "DEAD=missing" means to apply all of the above as long as the left hand member is not already in the X11 keymap.

-norepeat, -repeat

Option -norepeat disables X server key auto repeat when

VNC clients are connected and VNC keyboard input is not idle for more than 5 minutes. This works around a repeating keystrokes bug (triggered by long processing delays between key down and key up client events: either from large screen changes or high latency). Default: -norepeat

Note: your VNC viewer side will likely do autorepeating,

so this is no loss unless someone is simultaneously at the real X display.

Use "-norepeat N" to set how many times norepeat will

be reset if something else (e.g. X session manager) undoes it. The default is 2. Use a negative value for unlimited resets.

-nofb

Ignore video framebuffer: only process keyboard and

pointer. Intended for use with Win2VNC and x2vnc dual-monitor setups.

-nobell

Do not watch for XBell events. (no beeps will be heard)

Note: XBell monitoring requires the XKEYBOARD extension.

-nosel

Do not manage exchange of X selection/cutbuffer between

VNC viewers and the X server at all.

-noprimary

Do not poll the PRIMARY selection for changes to send

back to clients. (PRIMARY is still set on received changes, however).

-nosetprimary

Do not set the PRIMARY selection for changes received

from VNC clients.

-noclipboard

Do not poll the CLIPBOARD selection for changes to send

back to clients. (CLIPBOARD is still set on received changes, however).

-nosetclipboard

Do not set the CLIPBOARD selection for changes

received from VNC clients.

-seldir string

If direction string is "send", only send the selection

to viewers, and if it is "recv" only receive it from viewers. To work around apps setting the selection too frequently and messing up the other end. You can actually supply a comma separated list of directions, including "debug" to turn on debugging output.

-cursor [mode], -nocursor

Sets how the pointer cursor shape (little icon at the

mouse pointer) should be handled. The "mode" string is optional and is described below. The default is to show some sort of cursor shape(s). How this is done depends on the VNC viewer and the X server. Use -nocursor to disable cursor shapes completely.

Some VNC viewers support the TightVNC CursorPosUpdates

and CursorShapeUpdates extensions (cuts down on network traffic by not having to send the cursor image every time the pointer is moved), in which case these extensions are used (see -nocursorshape and -nocursorpos below to disable). For other viewers the cursor shape is written directly to the framebuffer every time the pointer is moved or changed and gets sent along with the other framebuffer updates. In this case, there will be some lag between the vnc viewer pointer and the remote cursor position.

If the X display supports retrieving the cursor shape

information from the X server, then the default is to use that mode. On Solaris this can be done with the SUN_OVL extension using -overlay (see also the -overlay_nocursor option). A similar overlay scheme is used on IRIX. Xorg (e.g. Linux) and recent Solaris Xsun servers support the XFIXES extension to retrieve the exact cursor shape from the X server. If XFIXES is present it is preferred over Overlay and is used by default (see -noxfixes below). This can be disabled with -nocursor, and also some values of the "mode" option below.

Note that under XFIXES cursors with transparency (alpha

channel) will usually not be exactly represented and one may find Overlay preferable. See also the -alphacut and -alphafrac options below as fudge factors to try to improve the situation for cursors with transparency for a given theme.

The "mode" string can be used to fine-tune the

displaying of cursor shapes. It can be used the following ways:

"-cursor arrow" - just show the standard arrow

nothing more or nothing less.

"-cursor none" - same as "-nocursor"

"-cursor X" - when the cursor appears to be on the

root window, draw the familiar X shape. Some desktops such as GNOME cover up the root window completely, and so this will not work, try "X1", etc, to try to shift the tree depth. On high latency links or slow machines there will be a time lag between expected and the actual cursor shape.

"-cursor some" - like "X" but use additional

heuristics to try to guess if the window should have a windowmanager-like resizer cursor or a text input I-beam cursor. This is a complete hack, but may be useful in some situations because it provides a little more feedback about the cursor shape.

"-cursor most" - try to show as many cursors as

possible. Often this will only be the same as "some" unless the display has overlay visuals or XFIXES extensions available. On Solaris and IRIX if XFIXES is not available, -overlay mode will be attempted.

-cursor_drag

Show cursor shape changes even when the mouse is being

dragged with a mouse button down. This is useful if you want to be able to see Drag-and-Drop cursor icons, etc.

-arrow n

Choose an alternate "arrow" cursor from a set of

some common ones. n can be 1 to 6. Default is: 1 Ignored when in XFIXES cursor-grabbing mode.

-noxfixes

Do not use the XFIXES extension to draw the exact cursor

shape even if it is available.

-alphacut n

When using the XFIXES extension for the cursor shape,

cursors with transparency will not usually be displayed exactly (but opaque ones will). This option sets n as a cutoff for cursors that have transparency ("alpha channel" with values ranging from 0 to 255) Any cursor pixel with alpha value less than n becomes completely transparent. Otherwise the pixel is completely opaque. Default 240

-alphafrac fraction

With the threshold in -alphacut some cursors will become

almost completely transparent because their alpha values are not high enough. For those cursors adjust the alpha threshold until fraction of the non-zero alpha channel pixels become opaque. Default 0.33

-alpharemove

By default, XFIXES cursors pixels with transparency have

the alpha factor multiplied into the RGB color values (i.e. that corresponding to blending the cursor with a black background). Specify this option to remove the alpha factor. (useful for light colored semi-transparent cursors).

-noalphablend

In XFIXES mode do not send cursor alpha channel data

to libvncserver. The default is to send it. The alphablend effect will only be visible in -nocursorshape mode or for clients with cursorshapeupdates turned off. (However there is a hack for 32bpp with depth 24, it uses the extra 8 bits to store cursor transparency for use with a hacked vncviewer that applies the transparency locally. See the FAQ for more info).

-nocursorshape

Do not use the TightVNC CursorShapeUpdates extension

even if clients support it. See -cursor above.

-cursorpos, -nocursorpos

Option -cursorpos enables sending the X cursor position

back to all vnc clients that support the TightVNC CursorPosUpdates extension. Other clients will be able to see the pointer motions. Default: -cursorpos

-xwarppointer, -noxwarppointer

Move the pointer with

XWarpPointer(3X) instead of the XTEST extension. Use this as a workaround if the pointer motion behaves incorrectly, e.g. on touchscreens or other non-standard setups.

It is also sometimes needed on XINERAMA displays and is

enabled by default if XINERAMA is found to be active. To prevent this, use -noxwarppointer.

-buttonmap string

String to remap mouse buttons. Format: IJK-LMN, this

maps buttons I -> L, etc., e.g. -buttonmap 13-31

Button presses can also be mapped to keystrokes: replace

a button digit on the right of the dash with :<sym>: or :<sym1>+<sym2>: etc. for multiple keys. For example, if the viewing machine has a mouse-wheel (buttons 4 5) but the x11vnc side does not, these will do scrolls:

-buttonmap 12345-123:Prior::Next:

-buttonmap 12345-123:Up+Up+Up::Down+Down+Down:

See <X11/keysymdef.h> header file for a list of Keysyms,

or use the xev(1) program. Note: mapping of button clicks to Keysyms may not work if -modtweak or -xkb is needed for the Keysym.

If you include a modifier like "Shift_L" the

modifier's up/down state is toggled, e.g. to send "The" use :Shift_L+t+Shift_L+h+e: (the 1st one is shift down and the 2nd one is shift up). (note: the initial state of the modifier is ignored and not reset) To include button events use "Button1", ... etc.

-nodragging

Do not update the display during mouse dragging events

(mouse button held down). Greatly improves response on slow setups, but you lose all visual feedback for drags, text selection, and some menu traversals. It overrides any -pointer_mode setting.

-ncache n

Client-side caching scheme. Framebuffer memory n

(an integer) times that of the full display is allocated below the actual framebuffer to cache screen contents for rapid retrieval. So a W x H frambuffer is expanded to a W x (n+1)*H one. Use 0 to disable. Default: XXX.

The n is actually optional, the default is 10.

For this and the other -ncache* options below you can

abbreviate "-ncache" with "-nc". Also, "-nonc" is the same as "-ncache 0"

This is an experimental option, currently implemented

in an awkward way in that in the VNC Viewer you can see the cache contents if you scroll down, etc. So you will have to set things up so you can't see that region. If this method is successful, the changes required for clients to do this less awkwardly will be investigated.

Note that this mode consumes a huge amount of memory,

both on the x11vnc server side and on the VNC Viewer side. If n=2 then the amount of RAM used is roughly tripled for both x11vnc and the VNC Viewer. As a rule of thumb, note that 1280x1024 at depth 24 is about 5MB of pixel data.

For reasonable response when cycling through 4 to 6

large (e.g. web browser) windows a value n of 6 to 12 is recommended. (that's right: ~10X more memory...)

Because of the way window backingstore and saveunders

are implemented, n must be even. It will be incremented by 1 if it is not.

This mode also works for native MacOS X, but may not

be as effective as the X version. This is due to a number of things, one is the drop-shadow compositing that leaves extra areas that need to be repaired (see -ncache_pad). Another is the window iconification animations need to be avoided (see -macicontime). It appears the that the 'Scale' animation mode gives better results than the 'Genie' one. Also, window event detection not as accurate as the X version.

-ncache_cr

In -ncache mode, try to do copyrect opaque window

moves/drags instead of wireframes (this can induce painting errors). The wireframe will still be used when moving a window whose save-unders has not yet been set or has been invalidated.

Some VNC Viewers provide better response than others

with this option. On Unix, realvnc viewer gives smoother drags than tightvnc viewer. Response may also be choppy if the server side machine is too slow.

Sometimes on very slow modem connections, this actually

gives an improvement because no pixel data at all (not even the box animation) is sent during the drag.

-ncache_no_moveraise

In -ncache mode, do not assume that moving a window

will cause the window manager to raise it to the top of the stack. The default is to assume it does, and so at the beginning of any wireframe, etc, window moves the window will be pushed to top in the VNC viewer.

-ncache_no_dtchange

In -ncache mode, do not try to guess when the desktop

(viewport) changes to another one (i.e. another workarea). The default is to try to guess and when detected try to make the transistion more smoothly.

-ncache_no_rootpixmap

In -ncache mode, do not try to snapshot the desktop

background to use in guessing or reconstructing window save-unders.

-ncache_keep_anims

In -ncache mode, do not try to disable window

manager animations and other effects (that usually degrade ncache performance or cause painting errors). The default is to try to disable them on KDE (but not GNOME) when VNC clients are connected.

For other window managers or desktops that provide

animations, effects, compositing, translucency, etc. that interfere with the -ncache method you will have to disable them manually.

-ncache_old_wm

In -ncache mode, enable some heuristics for old style

window managers such as fvwm and twm.

-ncache_pad n

In -ncache mode, pad each window with n pixels for the

caching rectangles. This can be used to try to improve the situation with dropshadows or other compositing (e.g. MacOS X window manager), although it could make things worse. The default is 0 on Unix and 24 on MacOS X.

-debug_ncache

Turn on debugging and profiling output under -ncache.

-wireframe [str], -nowireframe

Try to detect window moves or resizes when a mouse

button is held down and show a wireframe instead of the full opaque window. This is based completely on heuristics and may not always work: it depends on your window manager and even how you move things around. See -pointer_mode below for discussion of the "bogging down" problem this tries to avoid. Default: -wireframe

Shorter aliases: -wf [str] and -nowf

The value "str" is optional and, of course, is

packed with many tunable parameters for this scheme:

Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4

Default: 0xff,2,0,32+8+8+8,all,0.15+0.30+5.0+0.125

If you leave nothing between commas: ",," the default

value is used. If you don't specify enough commas, the trailing parameters are set to their defaults.

"shade" indicate the "color" for the wireframe,

usually a greyscale: 0-255, however for 16 and 32bpp you can specify an rgb.txt X color (e.g. "dodgerblue") or a value > 255 is treated as RGB (e.g. red is 0xff0000). "linewidth" sets the width of the wireframe in pixels. "percent" indicates to not apply the wireframe scheme to windows with area less than this percent of the full screen.

"T+B+L+R" indicates four integers for how close in

pixels the pointer has to be from the Top, Bottom, Left, or Right edges of the window to consider wireframing. This is a speedup to quickly exclude a window from being wireframed: set them all to zero to not try the speedup (scrolling and selecting text will likely be slower).

"mod" specifies if a button down event in the

interior of the window with a modifier key (Alt, Shift, etc.) down should indicate a wireframe opportunity. It can be "0" or "none" to skip it, "1" or "all" to apply it to any modifier, or "Shift", "Alt", "Control", "Meta", "Super", or "Hyper" to only apply for that type of modifier key.

"t1+t2+t3+t4" specify four floating point times in

seconds: t1 is how long to wait for the pointer to move, t2 is how long to wait for the window to start moving or being resized (for some window managers this can be rather long), t3 is how long to keep a wireframe moving before repainting the window. t4 is the minimum time between sending wireframe "animations". If a slow link is detected, these values may be automatically changed to something better for a slow link.

-nowireframelocal

By default, mouse motion and button presses of a

user sitting at the LOCAL display are monitored for wireframing opportunities (so that the changes will be sent efficiently to the VNC clients). Use this option to disable this behavior.

-wirecopyrect mode, -nowirecopyrect

Since the -wireframe mechanism evidently tracks moving

windows accurately, a speedup can be obtained by telling the VNC viewers to locally copy the translated window region. This is the VNC CopyRect encoding: the framebuffer update doesn't need to send the actual new image data.

Shorter aliases: -wcr [mode] and -nowcr

"mode" can be "never" (same as -nowirecopyrect)

to never try the copyrect, "top" means only do it if the window was not covered by any other windows, and "always" means to translate the orginally unobscured region (this may look odd as the remaining pieces come in, but helps on a slow link). Default: "always"

Note: there can be painting errors or slow response

when using -scale so you may want to disable CopyRect in this case "-wirecopyrect never" on the command line or by remote-control. Or you can also use the "-scale xxx:nocr" scale option.

-debug_wireframe

Turn on debugging info printout for the wireframe

heuristics. "-dwf" is an alias. Specify multiple times for more output.

-scrollcopyrect mode, -noscrollcopyrect

Like -wirecopyrect, but use heuristics to try to guess

if a window has scrolled its contents (either vertically or horizontally). This requires the RECORD X extension to "snoop" on X applications (currently for certain XCopyArea and XConfigureWindow X protocol requests). Examples: Hitting <Return> in a terminal window when the cursor was at the bottom, the text scrolls up one line. Hitting <Down> arrow in a web browser window, the web page scrolls up a small amount. Or scrolling with a scrollbar or mouse wheel.

Shorter aliases: -scr [mode] and -noscr

This scheme will not always detect scrolls, but when

it does there is a nice speedup from using the VNC CopyRect encoding (see -wirecopyrect). The speedup is both in reduced network traffic and reduced X framebuffer polling/copying. On the other hand, it may induce undesired transients (e.g. a terminal cursor being scrolled up when it should not be) or other painting errors (window tearing, bunching-up, etc). These are automatically repaired in a short period of time. If this is unacceptable disable the feature with -noscrollcopyrect.

Screen clearing kludges: for testing at least, there

are some "magic key sequences" (must be done in less than 1 second) to aid repairing painting errors that may be seen when using this mode:

3 Alt_L's in a row: resend whole screen,

4 Alt_L's in a row: reread and resend whole screen, 3 Super_L's in a row: mark whole screen for polling, 4 Super_L's in a row: reset RECORD context, 5 Super_L's in a row: try to push a black screen

note: Alt_L is the Left "Alt" key (a single key)

Super_L is the Left "Super" key (Windows flag). Both of these are modifier keys, and so should not generate characters when pressed by themselves. Also, your VNC viewer may have its own refresh hot-key or button.

"mode" can be "never" (same as -noscrollcopyrect)

to never try the copyrect, "keys" means to try it in response to keystrokes only, "mouse" means to try it in response to mouse events only, "always" means to do both. Default: "always"

Note: there can be painting errors or slow response

when using -scale so you may want to disable CopyRect in this case "-scrollcopyrect never" on the command line or by remote-control. Or you can also use the "-scale xxx:nocr" scale option.

-scr_area n

Set the minimum area in pixels for a rectangle

to be considered for the -scrollcopyrect detection scheme. This is to avoid wasting the effort on small rectangles that would be quickly updated the normal way. E.g. suppose an app updated the position of its skinny scrollbar first and then shifted the large panel it controlled. We want to be sure to skip the small scrollbar and get the large panel. Default: 60000

-scr_skip list

Skip scroll detection for applications matching

the comma separated list of strings in list. Some applications implement their scrolling in strange ways where the XCopyArea, etc, also applies to invisible portions of the window: if we CopyRect those areas it looks awful during the scroll and there may be painting errors left after the scroll. Soffice.bin is the worst known offender.

Use "##" to denote the start of the application class

(e.g. "##XTerm") and "++" to denote the start of the application instance name (e.g. "++xterm"). The string your list is matched against is of the form "^^WM_NAME##Class++Instance<same-for-any-subwindows>" The "xlsclients -la" command will provide this info.

If a pattern is prefixed with "KEY:" it only applies

to Keystroke generated scrolls (e.g. Up arrow). If it is prefixed with "MOUSE:" it only applies to Mouse induced scrolls (e.g. dragging on a scrollbar). Default: ##Soffice.bin,##StarOffice

-scr_inc list

Opposite of -scr_skip: this list is consulted first

and if there is a match the window will be monitored via RECORD for scrolls irrespective of -scr_skip. Use -scr_skip '*' to skip anything that does not match your -scr_inc. Use -scr_inc '*' to include everything.

-scr_keys list

For keystroke scroll detection, only apply the RECORD

heuristics to the comma separated list of keysyms in list. You may find the RECORD overhead for every one of your keystrokes disrupts typing too much, but you don't want to turn it off completely with "-scr mouse" and -scr_parms does not work or is too confusing.

The listed keysyms can be numeric or the keysym

names in the <X11/keysymdef.h> header file or from the xev(1) program. Example: "-scr_keys Up,Down,Return". One probably wants to have application specific lists (e.g. for terminals, etc) but that is too icky to think about for now...

If list begins with the "-" character the list

is taken as an exclude list: all keysyms except those list will be considered. The special string "builtin" expands to an internal list of keysyms that are likely to cause scrolls. BTW, by default modifier keys, Shift_L, Control_R, etc, are skipped since they almost never induce scrolling by themselves.

-scr_term list

Yet another cosmetic kludge. Apply shell/terminal

heuristics to applications matching comma separated list (same as for -scr_skip/-scr_inc). For example an annoying transient under scroll detection is if you hit Enter in a terminal shell with full text window, the solid text cursor block will be scrolled up. So for a short time there are two (or more) block cursors on the screen. There are similar scenarios, (e.g. an output line is duplicated).

These transients are induced by the approximation of

scroll detection (e.g. it detects the scroll, but not the fact that the block cursor was cleared just before the scroll). In nearly all cases these transient errors are repaired when the true X framebuffer is consulted by the normal polling. But they are distracting, so what this option provides is extra "padding" near the bottom of the terminal window: a few extra lines near the bottom will not be scrolled, but rather updated from the actual X framebuffer. This usually reduces the annoying artifacts. Use "none" to disable. Default: "term"

-scr_keyrepeat lo-hi

If a key is held down (or otherwise repeats rapidly) and

this induces a rapid sequence of scrolls (e.g. holding down an Arrow key) the "scrollcopyrect" detection and overhead may not be able to keep up. A time per single scroll estimate is performed and if that estimate predicts a sustainable scrollrate of keys per second between "lo" and "hi" then repeated keys will be DISCARDED to maintain the scrollrate. For example your key autorepeat may be 25 keys/sec, but for a large window or slow link only 8 scrolls per second can be sustained, then roughly 2 out of every 3 repeated keys will be discarded during this period. Default: "4-20"

-scr_parms string

Set various parameters for the scrollcopyrect mode.

The format is similar to that for -wireframe and packed with lots of parameters:

Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5

Default: 0+64+32+32,0.02+0.10+0.9,0.03+0.06+0.5+0.1+5.0

If you leave nothing between commas: ",," the default

value is used. If you don't specify enough commas, the trailing parameters are set to their defaults.

"T+B+L+R" indicates four integers for how close in

pixels the pointer has to be from the Top, Bottom, Left, or Right edges of the window to consider scrollcopyrect. If -wireframe overlaps it takes precedence. This is a speedup to quickly exclude a window from being watched for scrollcopyrect: set them all to zero to not try the speedup (things like selecting text will likely be slower).

"t1+t2+t3" specify three floating point times in

seconds that apply to scrollcopyrect detection with *Keystroke* input: t1 is how long to wait after a key is pressed for the first scroll, t2 is how long to keep looking after a Keystroke scroll for more scrolls. t3 is how frequently to try to update surrounding scrollbars outside of the scrolling area (0.0 to disable)

"s1+s2+s3+s4+s5" specify five floating point times

in seconds that apply to scrollcopyrect detection with *Mouse* input: s1 is how long to wait after a mouse button is pressed for the first scroll, s2 is how long to keep waiting for additional scrolls after the first Mouse scroll was detected. s3 is how frequently to try to update surrounding scrollbars outside of the scrolling area (0.0 to disable). s4 is how long to buffer pointer motion (to try to get fewer, bigger mouse scrolls). s5 is the maximum time to spend just updating the scroll window without updating the rest of the screen.

-fixscreen string

Periodically "repair" the screen based on settings

in string. Hopefully you won't need this option, it is intended for cases when the -scrollcopyrect or -wirecopyrect features leave too many painting errors, but it can be used for any scenario. This option periodically performs costly operations and so interactive response may be reduced when it is on. You can use 3 Alt_L's (the Left "Alt" key) taps in a row (as described under -scrollcopyrect) instead to manually request a screen repaint when it is needed.

string is a comma separated list of one or more of

the following: "V=t", "C=t", "X=t", and "8=t". In these "t" stands for a time in seconds (it is a floating point even though one should usually use values > 2 to avoid wasting resources). V sets how frequently the entire screen should be sent to viewers (it is l