lshell(1)

General Commands Manual

lshell(1)

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
--<param> <value>: where <param> is *any* config file parameter
-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

The configuration is dynamically reloaded. Which means that you can edit the configuration, and all the connected users will automatically load it. In case you are using multiple configuration files (see include_dir), you will need to refresh the main configuration's timestamp, in order to reload the configuration:

touch /path/to/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)
include_dir: include a directory containing multiple configuration files. These files can only contain default/user/group configuration. The global configuration will only be loaded from the default configuration file. This variable will be expanded (e.g. /path/*.conf).
path_noexec: set path to sudo noexec library. This path is usually autodetected, only set this variable to use alternate path. If set and the shared object is not found, lshell will exit immediately. Otherwise, please check your logs to verify that a standard path is detected.

[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
if sudo(8) is installed and sudo_noexec.so is available, it will be loaded before running every command, preventing it from running further commands itself. If not available, beware of commands like vim/find/more/etc. that will allow users to execute code (e.g. /bin/sh) from within the application, thus easily escaping lshell. See variable 'path_noexec' to use an alternative path to library.
allowed_shell_escape: a list of the allowed commands that are permitted to execute other programs (e.g. shell scripts with exec(3)). Setting this variable to 'all' is NOT allowed. Warning: do not put here any command that can execute arbitrary commands (e.g. find, vim, xargs).
important: commands defined in 'allowed_shell_escape' override their definition in the ´allowed´ variable.
allowed_cmd_path: a list of path; all executable files inside these path will be allowed
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
login_script: define the script to run at user login
passwd: password of specific user (default is empty)
path: list of path to restrict the user geographically. It is possible to use wildcards (e.g. '/var/log/ap*').
prompt: set the user's prompt format (default: username)

%u -> username

%h -> hostname

prompt_short: set prompt style for current directory - 0, 1 or 2. Default is 0.

0 -> will show the current directory as compared to home directory ~/current/dir

1 -> will only show the current directory name

2 -> will show the complete path to the current directory

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.
WARNING: This option will not work if you are using OpenSSH's internal-sftp service (e.g. when configured in chroot)
sudo_commands: a list of the allowed commands that can be used with sudo(8). If set to ´all', all the 'allowed' commands will be accessible through sudo(8).
It is possible to use the -u sudo flag in order to run a command as a different user than the default root.
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.
winscp: enable support for WinSCP with scp mode (NOT sftp)
When enabled, the following parameters will be overridden:

scp_upload: 1 (uses scp(1) from within session)

scp_download: 1 (uses scp(1) from within session)

scpforce: ignored (uses scp(1) from within session)

forbidden: -[';']

allowed: +['scp', 'env', 'pwd', 'groups', 'unset', 'unalias']

SHELL BUILTIN COMMANDS¶

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

clear: clears the terminal
export: name of exported shell variable. Disabled by default, enable it by adding it to allowed commands.
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:

# addgroup --system lshell
# 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>

July, 2015

v0.9.18

Source file:	lshell.1.en.gz (from lshell )
Source last updated:	2016-02-26T23:29:00Z
Converted to HTML:	2022-09-07T22:56:00Z