Change user ID or become superuser with the command : su
Posted by on Saturday, December 12, 2009 Under: Terminal Commands
NAME
su - change user ID or become superuser
SYNOPSIS
su [options] [username]
DESCRIPTION
The su command is used to become another user during a login session. Invoked without a username, su defaults to
becoming the superuser. The optional argument - may be used to provide an environment similar to what the user
would expect had the user logged in directly.
Additional arguments may be provided after the username, in which case they are supplied to the user´s login
shell. In particular, an argument of -c will cause the next argument to be treated as a command by most command
interpreters. The command will be executed by the shell specified in /etc/passwd for the target user.
You can use the -- argument to separate su options from the arguments supplied to the shell.
The user will be prompted for a password, if appropriate. Invalid passwords will produce an error message. All
attempts, both valid and invalid, are logged to detect abuse of the system.
The current environment is passed to the new shell. The value of $PATH is reset to /bin:/usr/bin for normal users,
or /sbin:/bin:/usr/sbin:/usr/bin for the superuser. This may be changed with the ENV_PATH and ENV_SUPATH
definitions in /etc/login.defs.
A subsystem login is indicated by the presence of a "*" as the first character of the login shell. The given home
directory will be used as the root of a new file system which the user is actually logged into.
OPTIONS
The options which apply to the su command are:
-c, --command COMMAND
Specify a command that will be invoked by the shell using its -c.
-, -l, --login
Provide an environment similar to what the user would expect had the user logged in directly.
When - is used, it must be specified as the last su option. The other forms (-l and --login) do not have this
restriction.
-s, --shell SHELL
The shell that will be invoked.
The invoked shell is chosen from (highest priority first):
· The shell specified with --shell.
· If --preserve-environment is used, the shell specified by the $SHELL environment variable.
· The shell indicated in the /etc/passwd entry for the target user.
· /bin/sh if a shell could not be found by any above method.
If the target user has a restricted shell (i.e. the shell field of this user´s entry in /etc/passwd is not
listed in /etc/shell), then the --shell option or the $SHELL environment variable won´t be taken into
account, unless su is called by root.
-m, -p, --preserve-environment
Preserve the current environment.
If the target user has a restricted shell, this option has no effect (unless su is called by root).
CAVEATS
This version of su has many compilation options, only some of which may be in use at any particular site.
CONFIGURATION
The following configuration variables in /etc/login.defs change the behavior of this tool:
CONSOLE_GROUPS (string)
List of groups to add to the user´s supplementary groups set when logging in on the console (as determined by
the CONSOLE setting). Default is none.
Use with caution - it is possible for users to gain permanent access to these groups, even when not logged in
on the console.
DEFAULT_HOME (boolean)
Indicate if login is allowed if we can´t cd to the home directory. Default in no.
If set to yes, the user will login in the root (/) directory if it is not possible to cd to her home
directory.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable when a regular user login. The value can be
preceded by PATH=, or a colon separated list of paths (for example /bin:/usr/bin). The default value is
PATH=/bin:/usr/bin.
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable when the superuser login. The value can be
preceded by PATH=, or a colon separated list of paths (for example /sbin:/bin:/usr/sbin:/usr/bin). The default
value is PATH=/bin:/usr/bin.
SULOG_FILE (string)
If defined, all su activity is logged to this file.
SU_NAME (string)
If defined, the command name to display when running "su -". For example, if this is defined as "su" then a
"ps" will display the command is "-su". If not defined, then "ps" would display the name of the shell actually
being run, e.g. something like "-sh".
SYSLOG_SU_ENAB (boolean)
Enable "syslog" logging of su activity - in addition to sulog file logging.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
su - change user ID or become superuser
SYNOPSIS
su [options] [username]
DESCRIPTION
The su command is used to become another user during a login session. Invoked without a username, su defaults to
becoming the superuser. The optional argument - may be used to provide an environment similar to what the user
would expect had the user logged in directly.
Additional arguments may be provided after the username, in which case they are supplied to the user´s login
shell. In particular, an argument of -c will cause the next argument to be treated as a command by most command
interpreters. The command will be executed by the shell specified in /etc/passwd for the target user.
You can use the -- argument to separate su options from the arguments supplied to the shell.
The user will be prompted for a password, if appropriate. Invalid passwords will produce an error message. All
attempts, both valid and invalid, are logged to detect abuse of the system.
The current environment is passed to the new shell. The value of $PATH is reset to /bin:/usr/bin for normal users,
or /sbin:/bin:/usr/sbin:/usr/bin for the superuser. This may be changed with the ENV_PATH and ENV_SUPATH
definitions in /etc/login.defs.
A subsystem login is indicated by the presence of a "*" as the first character of the login shell. The given home
directory will be used as the root of a new file system which the user is actually logged into.
OPTIONS
The options which apply to the su command are:
-c, --command COMMAND
Specify a command that will be invoked by the shell using its -c.
-, -l, --login
Provide an environment similar to what the user would expect had the user logged in directly.
When - is used, it must be specified as the last su option. The other forms (-l and --login) do not have this
restriction.
-s, --shell SHELL
The shell that will be invoked.
The invoked shell is chosen from (highest priority first):
· The shell specified with --shell.
· If --preserve-environment is used, the shell specified by the $SHELL environment variable.
· The shell indicated in the /etc/passwd entry for the target user.
· /bin/sh if a shell could not be found by any above method.
If the target user has a restricted shell (i.e. the shell field of this user´s entry in /etc/passwd is not
listed in /etc/shell), then the --shell option or the $SHELL environment variable won´t be taken into
account, unless su is called by root.
-m, -p, --preserve-environment
Preserve the current environment.
If the target user has a restricted shell, this option has no effect (unless su is called by root).
CAVEATS
This version of su has many compilation options, only some of which may be in use at any particular site.
CONFIGURATION
The following configuration variables in /etc/login.defs change the behavior of this tool:
CONSOLE_GROUPS (string)
List of groups to add to the user´s supplementary groups set when logging in on the console (as determined by
the CONSOLE setting). Default is none.
Use with caution - it is possible for users to gain permanent access to these groups, even when not logged in
on the console.
DEFAULT_HOME (boolean)
Indicate if login is allowed if we can´t cd to the home directory. Default in no.
If set to yes, the user will login in the root (/) directory if it is not possible to cd to her home
directory.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable when a regular user login. The value can be
preceded by PATH=, or a colon separated list of paths (for example /bin:/usr/bin). The default value is
PATH=/bin:/usr/bin.
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable when the superuser login. The value can be
preceded by PATH=, or a colon separated list of paths (for example /sbin:/bin:/usr/sbin:/usr/bin). The default
value is PATH=/bin:/usr/bin.
SULOG_FILE (string)
If defined, all su activity is logged to this file.
SU_NAME (string)
If defined, the command name to display when running "su -". For example, if this is defined as "su" then a
"ps" will display the command is "-su". If not defined, then "ps" would display the name of the shell actually
being run, e.g. something like "-sh".
SYSLOG_SU_ENAB (boolean)
Enable "syslog" logging of su activity - in addition to sulog file logging.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
In : Terminal Commands