man : su(1)
SU(1) OpenBSD Reference Manual SU(1)
su - substitute user identity
su [-fKLlm] [-a auth-type] [-c login-class] [-s login-shell]
[login [shell arguments]]
The su utility allows a user to run a shell with the user and group ID of
another user without having to log out and in as that other user.
If Kerberos is in use, the password for login (or for ``login/root'', if
no login is provided) is requested, and su switches to that user and
group ID after obtaining a Kerberos ticket granting access. A shell is
then executed, and any additional shell arguments after the login name
are passed to the shell. If Kerberos is not configured or if there is a
Kerberos error, su falls back to local password authentication to
validate the password for login. 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 LOGNAME,
HOME, SHELL, and USER. HOME and SHELL are set to the target login's
default values. LOGNAME and USER are set to the target login, unless the
target login has a user ID of 0 and the -l flag was not specified, in
which case it is unmodified. The invoked shell is the target login's.
This is the traditional behavior of su.
If not using -m and the target login has a user ID of 0 then the PATH
variable and umask value (see umask(2)) are always set according to the
/etc/login.conf file (see login.conf(5)).
The options are as follows:
- Same as the -l option (deprecated).
Specify an authentication type such as ``skey'', ``securid'', or
Specify a login class. You may only override the default class
if you're already root.
-f If the invoked shell is csh(1), this option prevents it from
reading the ``.cshrc'' file.
-K Do not attempt to use Kerberos to authenticate the user. This is
shorthand for ``su -a passwd'', provided for backwards
-L Loop until a correct username and password combination is
entered, similar to login(1). Note that in this mode target
login must be specified explicitly, either on the command line or
interactively. Additionally, su will prompt for the password
even when invoked by root.
-l Simulate a full login. The environment is discarded except for
HOME, SHELL, PATH, TERM, LOGNAME, and USER. HOME and SHELL are
modified as above. LOGNAME and USER are set to the target login.
PATH is set to the value specified by the ``path'' entry in
login.conf(5). 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.
Specify the path to an alternate login shell. You may only
override the shell if you're already root. This option will
override the shell even if the -m option is specified.
The -l and -m options are mutually exclusive; the last one specified
overrides any previous ones.
If the optional shell arguments are provided on the command line, they
are passed to the login shell of the target login. This allows it to
pass arbitrary commands via the -c option as understood by most shells.
Note that -c usually expects a single argument only; you have to quote it
when passing multiple words.
If group 0 (normally ``wheel'') has users listed then only those users
can su to ``root''. It is not sufficient to change a user's /etc/passwd
entry to add them to the ``wheel'' group; they must explicitly be listed
in /etc/group. If no one is in the ``wheel'' group, it is ignored, and
anyone who knows the root password is permitted to su to ``root''.
By default (unless the prompt is reset by a startup file) the superuser
prompt is set to ``#'' to remind one of its awesome power.
HOME Default home directory of real user ID unless modified as
LOGNAME The user ID is always the effective ID (the target user ID)
after an su unless the user ID is 0 (root).
PATH Default search path of real user ID unless modified as specified
TERM Provides terminal type which may be retained for the substituted
USER Same as LOGNAME.
Run the command ``makewhatis'' as user ``bin''. You will be asked for
bin's password unless your real UID is 0.
$ su bin -c makewhatis
Same as above, but the target command consists of more than a single
$ su bin -c 'makewhatis /usr/local/man'
Same as above, but the target command is run with the resource limits of
the login class ``staff''. Note that the first -c option applies to su
while the second is an argument to the shell.
$ su -c staff bin -c 'makewhatis /usr/local/man'
Pretend a login for user ``foo'':
$ su -l foo
Same as above, but use S/Key for authentication:
$ su -a skey -l foo
csh(1), kinit(1), login(1), sh(1), skey(1), setusercontext(3), group(5),
login.conf(5), passwd(5), environ(7), sudo(8)
A su command appeared in Version 7 AT&T UNIX.
The login name is not optional for root if there are shell arguments.
OpenBSD 4.9 December 10, 2010 OpenBSD 4.9