SU(1) BSD Reference Manual SU(1)NAMEsu - substitute user identity
SYNOPSISsu [-fKLlm] [-a auth-type] [-c login-class] [login [shell arguments]]
DESCRIPTIONsu 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 access. A shell is then executed, and any
additional shell arguments after the login name are passed to the shell.
su will resort to the local password file to find the password for login
if there is a Kerberos error or if Kerberos is not installed. If su is
executed by root, no password is requested and a shell with the appropri-
ate 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 de-
fault 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).
-a auth-type
Specify an authentication type such as "skey", "securid", or
"krb5".
-c login-class
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.
-L Loop until a correct username and password combination is en-
tered, similar to login(1). Note that in this mode target login
must be specified explicitly, either on the command line or in-
teractively. 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 precau-
tion, if the target user's shell is a non-standard shell (as de-
fined 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.
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.
ENVIRONMENT
HOME Default home directory of real user ID unless modified as speci-
fied above.
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
above.
TERM Provides terminal type which may be retained for the substituted
user ID.
USER Same as LOGNAME.
EXAMPLES
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
word:
$ 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
SEE ALSOcsh(1), kinit(1), login(1), sh(1), skey(1), setusercontext(3), group(5),
login.conf(5), passwd(5), environ(7), sudo(8)HISTORY
A su command appeared in Version 7 AT&T UNIX.
BUGS
There is no direct way to force a particular shell to be used.
The login name is not optional for root if there are shell arguments.
MirOS BSD #10-current July 29, 1991 2
