SU(1) BSD General Commands Manual SU(1)NAMEsu — substitute user identity
SYNOPSISsu [-] [-flm] [login [args]]
DESCRIPTION
The su utility requests appropriate user credentials via PAM and switches
to that user ID (the default user is the superuser). A shell is then
executed.
PAM is used to set the policy su(1) will use. In particular, by default
only users in the “admin” or “wheel” groups can switch to UID 0 (“root”).
This group requirement may be changed by modifying the “pam_group” sec‐
tion of /etc/pam.d/su. See pam_group(8) for details on how to modify
this setting.
By default, the environment is unmodified with the exception of USER,
HOME, and SHELL. HOME and SHELL are set to the target login's default
values. USER is set to the target login, unless the target login has a
user ID of 0, in which case it is unmodified. The invoked shell is the
one belonging to the target login. This is the traditional behavior of
su.
The options are as follows:
-f If the invoked shell is csh(1), this option prevents it from
reading the “.cshrc” file.
-l Simulate a full login. The environment is discarded except for
HOME, SHELL, PATH, TERM, and USER. HOME and SHELL are modified
as above. USER is set to the target login. PATH is set to
“/bin:/usr/bin”. TERM is imported from your current environment.
The invoked shell is the target login's, and su will change
directory to the target login's home directory.
- (no letter) The same as -l.
-m Leave the environment unmodified. The invoked shell is your
login shell, and no directory changes are made. As a security
precaution, if the target user's shell is a non-standard shell
(as defined by getusershell(3)) and the caller's real uid is non-
zero, su will fail.
The -l (or -) and -m options are mutually exclusive; the last one speci‐
fied overrides any previous ones.
If the optional args are provided on the command line, they are passed to
the login shell of the target login. Note that all command line argu‐
ments before the target login name are processed by su itself, everything
after the target login name gets passed to the login shell.
By default (unless the prompt is reset by a startup file) the super-user
prompt is set to “#” to remind one of its awesome power.
ENVIRONMENT
Environment variables used by su:
HOME Default home directory of real user ID unless modified as specified
above.
PATH Default search path of real user ID unless modified as specified
above.
TERM Provides terminal type which may be retained for the substituted
user ID.
USER The user ID is always the effective ID (the target user ID) after
an su unless the user ID is 0 (root).
FILES
/etc/pam.d/su PAM configuration for su.
EXAMPLESsu man -c catman
Runs the command catman as user man. You will be asked for man's
password unless your real UID is 0.
su man -c 'catman /usr/share/man /usr/local/man'
Same as above, but the target command consists of more than a sin‐
gle word and hence is quoted for use with the -c option being
passed to the shell. (Most shells expect the argument to -c to be
a single word).
su-l foo
Simulate a login for user foo.
su - foo
Same as above.
su - Simulate a login for root.
SEE ALSOcsh(1), sh(1), group(5), passwd(5), environ(7), pam_group(8)HISTORY
A su command appeared in Version 1 AT&T UNIX.
BSD September 13, 2006 BSD
