SU
Section: User Commands (1)
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BSD mandoc
NAME
su
- substitute user identity
SYNOPSIS
su
[-Kflm
]
[login
]
DESCRIPTION
Su requests the Kerberos password for
login
(or for
``login .root
''
if no login is provided), and switches to
that user and group ID after obtaining a Kerberos ticket granting ticket.
A shell is then executed.
Su will resort to the local password file to find the password for
login
if there is a Kerberos error.
If
su
is executed by root, no password is requested and a shell
with the appropriate user ID is executed; no additional Kerberos tickets
are obtained.
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 target login's.
This is the traditional behavior of
su
The options are as follows:
- -K
-
Do not attempt to use Kerberos to authenticate the user.
- -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.
- -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
and
-m
options are mutually exclusive; the last one specified
overrides any previous ones.
Only users in group 0 (normally
``wheel''
can
su
to
``root''
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.
SEE ALSO
csh(1),
login(1),
sh(1),
kinit(1),
kerberos(1),
passwd(5),
group(5),
environ(7)
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).
HISTORY
A
su
command appeared in
AT&T System
v7 .
The version desribed
here is an adaptation of the
MIT
Athena Kerberos command.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- SEE ALSO
-
- ENVIRONMENT
-
- HISTORY
-
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Time: 06:34:25 GMT, May 19, 2025