table of contents
SU(1) | User Commands | SU(1) |
NAME¶
su - change user ID or become superuserSYNOPSIS¶
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 COMMANDSpecify a command that will be invoked by the
shell using its -c.
The executed command will have no controlling terminal. This option cannot be
used to execute interractive programs which need a controlling TTY.
-, -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):
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/shells), 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
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.
Preserve the current environment, except for:
$PATH
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:
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.
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 environments 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 is 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 is a colon separated
list of paths (for example /bin:/usr/bin) and can be preceded by
PATH=. 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 is a colon separated
list of paths (for example /sbin:/bin:/usr/sbin:/usr/bin) and can be
preceded by PATH=. The default value is
PATH=/sbin:/bin:/usr/sbin:/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/passwdUser account information.
/etc/shadow
Secure user account information.
/etc/login.defs
Shadow password suite configuration.
EXIT VALUES¶
On success, su returns the exit value of the command it executed. If this command was terminated by a signal, su returns the number of this signal plus 128. If su has to kill the command (because it was asked to terminate, and the command did not terminate in time), su returns 255. Some exit values from su are independent from the executed command: 0success (--help only)
1
System or authentication failure
126
The requested command was not found
127
The requested command could not be
executed
SEE ALSO¶
login(1), login.defs(5), sg(1), sh(1).05/25/2012 | shadow-utils 4.1.5.1 |