lshell(1) - Linux man page

Name

lshell - Limited Shell

Synopsis

lshell [OPTIONS]

Description

lshell provides a limited shell configured per user. The configuration is done quite simply using a configuration file. Coupled with ssh's authorized_keys or with /etc/shells and /etc/passwd , it becomes very easy to restrict user's access to a limited set of command.

Options

--config <FILE>: Specify config file
--log <DIR>: Specify the log directory
-h, --help: Show help message
--version: Show version

Configuration

You can configure lshell through its configuration file:

On Linux -> /etc/lshell.conf
On *BSD  -> /usr/{pkg,local}/etc/lshell.conf
lshell configuration has 4 types of sections:
[global]   -> lshell system configuration (only 1)
[default]  -> lshell default user configuration (only 1)
[foo]      -> UNIX username "foo" specific configuration
[grp:bar]  -> UNIX groupname "bar" specific configuration
Order of priority when loading preferences is the following:
1- User configuration
2- Group configuration
3- Default configuration
[global]

logpath
config path (default is /var/log/lshell/)
loglevel
0, 1, 2, 3 or 4 (0: no logs -> 4: logs everything)
logfilename
- set to syslog in order to log to syslog
- set log file name, e.g. %u-%y%m%d (i.e foo-20091009.log): %u ->
username
%d -> day [1..31]

%m -> month [1..12]

%y -> year [00..99]

%h -> time [00:00..23:59]

syslogname
in case you are using syslog, set your logname (default: lshell)
[default] and/or [username] and/or [grp:groupname]

aliases
command aliases list (similar to bash's alias directive)
allowed
a list of the allowed commands or set to 'all' to allow all commands in user's PATH
env_path
update the environment variable $PATH of the user (optional)
env_vars
set environment variables (optional)
forbidden
a list of forbidden characters or commands
history_file
set the history filename. A wildcard can be used:
%u -> username (e.g. '/home/%u/.lhistory')

history_size: set the maximum size (in lines) of the history file
home_path (deprecated): set the home folder of your user. If not specified, the home directory is set to the $HOME environment variable. This variable will be removed in the next version of lshell, please use your system's tools to set a user's home directory. A wildcard can be used:
%u -> username (e.g. '/home/%u')
intro: set the introduction to print at login
passwd: password of specific user (default is empty)
path: list of path to restrict the user geographically
prompt: set the user's prompt format (default: username)
%u ->

username

%h -> hostname

overssh: list of command allowed to execute over ssh (e.g. rsync, rdiff-backup, scp, etc.)
scp: allow or forbid the use of scp connection - set to 1 or 0
scpforce: force files sent through scp to a specific directory
scp_download: set to 0 to forbid scp downloads (default is 1)
scp_upload: set to 0 to forbid scp uploads (default is 1)
sftp: allow or forbid the use of sftp connection - set to 1 or 0
sudo_commands: a list of the allowed commands that can be used with sudo(8)
timer: a value in seconds for the session timer
strict: logging strictness. If set to 1, any unknown command is considered as forbidden, and user's warning counter is decreased. If set to 0, command is considered as unknown, and user is only warned (i.e. *** unknown synthax)
warning_counter: number of warnings when user enters a forbidden value before getting exited from lshell. Set to -1 to disable the counter, and just warn the user.

Shell Builtin Commands

Here is the set of commands that are always available with lshell:

clear: clears the terminal
help, ?: print the list of allowed commands
history: print the commands history
lpath: lists all allowed and forbidden path
lsudo: lists
all sudo allowed commands

Examples

$ lshell: Tries to run lshell using default ${PREFIX}/etc/lshell.conf as configuration file. If it fails a warning is printed and lshell is interrupted.

lshell options are loaded from the configuration file

$ lshell --config /path/to/myconf.file --log /path/to/mylog.log: This will override the default options specified for configuration and/or log

file

Use Case

The primary goal of lshell, was to be able to create shell accounts with ssh access and restrict their environment to a couple a needed commands. In this example, User 'foo' and user 'bar' both belong to the 'users' UNIX group:

User foo:: - must be able to access /usr and /var but not /usr/local
- user all command in his PATH but 'su'
- has a warning counter set to 5
- has his home path set to '/home/users'
User bar:: - must be able to access /etc and /usr but not /usr/local
- is allowed default commands plus 'ping' minus 'ls'
- strictness is set to 1 (meaning he is not allowed to type an unknown command)

In this case, my configuration file will look something like this:

# CONFIURATION START
[global]
logpath         : /var/log/lshell/
loglevel        : 2
[default]
allowed         : ['ls','pwd']
forbidden       : [';', '&', '|']
warning_counter : 2
timer           : 0
path            : ['/etc', '/usr']
env_path        : ':/sbin:/usr/bin/'
scp             : 1 # or 0
sftp            : 1 # or 0
overssh         : ['rsync','ls']
aliases         : {'ls':'ls --color=auto','ll':'ls -l'}
[grp:users]
warning_counter : 5
overssh         : - ['ls']
[foo]
allowed         : 'all' - ['su']
path            : ['/var', '/usr'] - ['/usr/local']
home_path       : '/home/users'
[bar]
allowed         : + ['ping'] - ['ls']
path            : - ['/usr/local']
strict          : 1
scpforce        : '/home/bar/uploads/'
# CONFIURATION END
Notes
In order to log a user's warnings into the logging directory (default
/var/log/lshell/) , you must firt create the folder (if it doesn't exist yet) and chown it to lshell group:
# mkdir /var/log/lshell
# chown :lshell /var/log/lshell
# chmod 770 /var/log/lshell
then add the user to the lshell group:
# usermod -aG lshell user_name
In order to set lshell as default shell for a user:
On Linux:
# chsh -s /usr/bin/lshell user_name
On *BSD:
# chsh -s /usr/{pkg,local}/bin/lshell user_name
Author
Currently maintained by Ignace Mouzannar (ghantoos)
Email
Feel free to send me your recommendations at <ghantoos@ghantoos.org>