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 users 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 users entry in /etc/passwd is not listed in /etc/shell), then
the --shell option or the $SHELL environment variable wont be taken
into account, unless su is called by root.
-m, -p, --preserve-environment
Preserve the current environment, except for:
$PATH
reset according to the /etc/login.defs options ENV_PATH or
ENV_SUPATH (see below);
$IFS
reset to "<space><tab><newline>", if it was set.
If the target user has a restricted shell, this option has no
effect (unless su is called by root).
Note that the default behavior for the environment is the
following:
The $HOME, $SHELL, $USER, $LOGNAME, $PATH, and $IFS environment
variables are reset.
If --login is not used, the environment is copied, except for
the variables above.
If --login is used, the $TERM, $COLORTERM, $DISPLAY, and
$XAUTHORITY environment variables are copied if they were set.
Other environment might be set by PAM modules.
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 users 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 cant 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.
/etc/login.defs
Shadow password suite configuration.
SEE ALSO
login(1), login.defs(5), sg(1), sh(1).