substitute user identity
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
will use. In particular, by default only users in the
” group can switch to UID 0
”). This group requirement may be
changed by modifying the “
section of /etc/pam.d/su
for details on how to modify this setting.
By default, the environment is unmodified with the exception of
are set to the target login's default
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
. Resource limits
and session priority applicable to the original user's login class (see
are also normally retained unless the target login has a user ID of 0.
The options are as follows:
- Use the settings of the specified login class. The login class must be
Only allowed for the super-user.
- If the invoked shell is
this option prevents it from reading the
- Simulate a full login. The environment is discarded except for
SHELL are modified as above.
USER is set to the target login.
PATH is set to
TERM is imported from your current
environment. Environment variables may be set or overridden from the login
class capabilities database according to the class of the target login.
The invoked shell is the target login's, and
su will change directory to the target
login's home directory. Resource limits and session priority are modified
to that for the target account's login class.
- (no letter) The same as
- 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
and the caller's real uid is non-zero,
su will fail.
- Set the MAC label to the user's default label as part of the user
credential setup. Setting the MAC label may fail if the MAC label of the
invoking process is not sufficient to transition to the user's default MAC
label. If the label cannot be set,
options are mutually exclusive; the last
one specified 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 arguments before the target login name are processed by
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
Environment variables used by
- Default home directory of real user ID unless modified as specified
- Default search path of real user ID unless modified as specified
- Provides terminal type which may be retained for the substituted user
- The user ID is always the effective ID (the target user ID) after an
su unless the user ID is 0 (root).
- PAM configuration for
-m operator -c poweroff
- Starts a shell as user
operator, and runs the
poweroff. You will be asked for operator's
password unless your real UID is 0. Note that the
-m option is required since user
“operator” does not have a valid shell by default. In this
-c is passed to the shell of
the user “operator”, and is not interpreted as an argument
-m operator -c 'shutdown -p now'
- Same as above, but the target command consists of more than a single word
and hence is quoted for use with the
option being passed to the shell. (Most shells expect the argument to
-c to be a single word).
-m -c staff operator -c 'shutdown -p now'
- Same as above, but the target command is run with the resource limits of
the login class “staff”. Note: in this example, the first
-c option applies to
su while the second is an argument to
the shell being invoked.
- Simulate a login for user foo.
- Same as above.
- Simulate a login for root.
command appeared in
Version 1 AT&T UNIX