1SU(1) User Commands SU(1)
2
6 su - run a command with substitute user and group ID
7
9 su [options] [-] [user [argument...]]
10
12 su allows commands to be run with a substitute user and group ID.
13 When called with no user specified, su defaults to running an
15 interactive shell as root. When user is specified, additional arguments
16 can be supplied, in which case they are passed to the shell.
17 For backward compatibility, su defaults to not change the current
19 directory and to only set the environment variables HOME and SHELL
20 (plus USER and LOGNAME if the target user is not root). It is
21 recommended to always use the --login option (instead of its shortcut
22 -) to avoid side effects caused by mixing environments.
23 This version of su uses PAM for authentication, account and session
25 management. Some configuration options found in other su
26 implementations, such as support for a wheel group, have to be
27 configured via PAM.
28 su is mostly designed for unprivileged users, the recommended solution
30 for privileged users (e.g., scripts executed by root) is to use
31 non-set-user-ID command runuser(1) that does not require authentication
32 and provides separate PAM configuration. If the PAM session is not
33 required at all then the recommended solution is to use command
34 setpriv(1).
35 Note that su in all cases uses PAM (pam_getenvlist(3)) to do the final
37 environment modification. Command-line options such as --login and
38 --preserve-environment affect the environment before it is modified by
39 PAM.
40 Since version 2.38 su resets process resource limits RLIMIT_NICE,
42 RLIMIT_RTPRIO, RLIMIT_FSIZE, RLIMIT_AS and RLIMIT_NOFILE.
43
45 -c, --command=command
46 Pass command to the shell with the -c option.
47 -f, --fast
49 Pass -f to the shell, which may or may not be useful, depending on
50 the shell.
51 -g, --group=group
53 Specify the primary group. This option is available to the root
54 user only.
55 -G, --supp-group=group
57 Specify a supplementary group. This option is available to the root
58 user only. The first specified supplementary group is also used as
59 a primary group if the option --group is not specified.
60 -, -l, --login
62 Start the shell as a login shell with an environment similar to a
63 real login:
64 • clears all the environment variables except TERM and variables
66 specified by --whitelist-environment
67 • initializes the environment variables HOME, SHELL, USER,
69 LOGNAME, and PATH
70 • changes to the target user’s home directory
72 • sets argv[0] of the shell to '-' in order to make the shell a
74 login shell
75 -m, -p, --preserve-environment
77 Preserve the entire environment, i.e., do not set HOME, SHELL, USER
78 or LOGNAME. This option is ignored if the option --login is
79 specified.
80 -P, --pty
82 Create a pseudo-terminal for the session. The independent terminal
83 provides better security as the user does not share a terminal with
84 the original session. This can be used to avoid TIOCSTI ioctl
85 terminal injection and other security attacks against terminal file
86 descriptors. The entire session can also be moved to the background
87 (e.g., su --pty - username -c application &). If the
88 pseudo-terminal is enabled, then su works as a proxy between the
89 sessions (sync stdin and stdout).
90 This feature is mostly designed for interactive sessions. If the
92 standard input is not a terminal, but for example a pipe (e.g.,
93 echo "date" | su --pty), then the ECHO flag for the pseudo-terminal
94 is disabled to avoid messy output.
95 -s, --shell=shell
97 Run the specified shell instead of the default. The shell to run is
98 selected according to the following rules, in order:
99 • the shell specified with --shell
101 • the shell specified in the environment variable SHELL, if the
103 --preserve-environment option is used
104 • the shell listed in the passwd entry of the target user
106 • /bin/sh
108 If the target user has a restricted shell (i.e., not listed in
110 /etc/shells), the --shell option and the SHELL environment variables
111 are ignored unless the calling user is root.
112 --session-command=command
114 Same as -c, but do not create a new session. (Discouraged.)
115 -w, --whitelist-environment=list
117 Don’t reset the environment variables specified in the
118 comma-separated list when clearing the environment for --login. The
119 whitelist is ignored for the environment variables HOME, SHELL,
120 USER, LOGNAME, and PATH.
121 -h, --help
123 Display help text and exit.
124 -V, --version
126 Print version and exit.
127
129 Upon receiving either SIGINT, SIGQUIT or SIGTERM, su terminates its
130 child and afterwards terminates itself with the received signal. The
131 child is terminated by SIGTERM, after unsuccessful attempt and 2
132 seconds of delay the child is killed by SIGKILL.
133
135 su reads the /etc/default/su and /etc/login.defs configuration files.
136 The following configuration items are relevant for su:
137 FAIL_DELAY (number)
139 Delay in seconds in case of an authentication failure. The number
140 must be a non-negative integer.
141 ENV_PATH (string)
143 Defines the PATH environment variable for a regular user. The
144 default value is /usr/local/bin:/bin:/usr/bin.
145 ENV_ROOTPATH (string), ENV_SUPATH (string)
147 Defines the PATH environment variable for root. ENV_SUPATH takes
148 precedence. The default value is
149 /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin.
150 ALWAYS_SET_PATH (boolean)
152 If set to yes and --login and --preserve-environment were not
153 specified su initializes PATH.
154 The environment variable PATH may be different on systems where
156 /bin and /sbin are merged into /usr; this variable is also affected
157 by the --login command-line option and the PAM system setting
158 (e.g., pam_env(8)).
159
161 su normally returns the exit status of the command it executed. If the
162 command was killed by a signal, su returns the number of the signal
163 plus 128.
164 Exit status generated by su itself:
166 1
168 Generic error before executing the requested command
169 126
171 The requested command could not be executed
172 127
174 The requested command was not found
175
177 /etc/pam.d/su
178 default PAM configuration file
179 /etc/pam.d/su-l
181 PAM configuration file if --login is specified
182 /etc/default/su
184 command specific logindef config file
185 /etc/login.defs
187 global logindef config file
188
190 For security reasons, su always logs failed log-in attempts to the btmp
191 file, but it does not write to the lastlog file at all. This solution
192 can be used to control su behavior by PAM configuration. If you want to
193 use the pam_lastlog(8) module to print warning message about failed
194 log-in attempts then pam_lastlog(8) has to be configured to update the
195 lastlog file as well. For example by:
196 session required pam_lastlog.so nowtmp
198
200 This su command was derived from coreutils' su, which was based on an
201 implementation by David MacKenzie. The util-linux version has been
202 refactored by Karel Zak.
203
205 setpriv(1), login.defs(5), shells(5), pam(8), runuser(1)
206
208 For bug reports, use the issue tracker at
209 https://github.com/util-linux/util-linux/issues.
210
212 The su command is part of the util-linux package which can be
213 downloaded from Linux Kernel Archive
214 <https://www.kernel.org/pub/linux/utils/util-linux/>.
215util-linux 2.38.1 2022-05-11 SU(1)