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, 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 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.
/etc/login.defs
-
Shadow password suite configuration.
SEE ALSO
login(1),
login.defs(5),
sg(1),
sh(1).
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- CAVEATS
-
- CONFIGURATION
-
- FILES
-
- SEE ALSO
-
This document was created by
man2html,
using the manual pages.
Time: 03:41:18 GMT, September 24, 2010