SU(1) BSD Reference Manual SU(1)
su - substitute user identity
su [-Kflm] [login]
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 obtain-
ing 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 re-
quested and a shell with the appropriate user ID is executed; no addi-
tional 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 environ-
ment. 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 lo-
gin shell, and no directory changes are made. As a security pre-
caution, 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.
csh(1), login(1), sh(1), kinit(1), kerberos(1), passwd(5),
Environment variables used by su:
HOME Default home directory of real user ID unless modified as specified
PATH Default search path of real user ID unless modified as specified
TERM 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).
A su command appeared in Version 7 AT&T UNIX.
4.4BSD April 18, 1994 2