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.\"	@(#)su.1	8.2 (Berkeley) 4/18/94
.\" $FreeBSD: src/usr.bin/su/su.1,v 1.17.2.6 2002/06/21 15:29:18 charnier Exp $
.\" $DragonFly: src/usr.bin/su/su.1,v 1.4 2006/02/17 19:39:11 swildner Exp $
.\"
.Dd April 18, 1994
.Dt SU 1
.Os
.Sh NAME
.Nm su
.Nd substitute user identity
.Sh SYNOPSIS
.Nm
.Op Fl
.Op Fl Kflm
.Op Fl c Ar class
.Op Ar login Op Ar args
.Sh DESCRIPTION
The
.Nm
utility requests the Kerberos password for
.Ar login
(or for
.Dq Ar login Ns .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.
The
.Nm
utility will resort to the local password file to find the password for
.Ar login
if there is a Kerberos error.
If
.Nm
is executed by root, no password is requested and a shell
with the appropriate user ID is executed; no additional Kerberos tickets
are obtained.
.Pp
By default, the environment is unmodified with the exception of
.Ev USER ,
.Ev HOME ,
and
.Ev SHELL .
.Ev HOME
and
.Ev SHELL
are set to the target login's default values.
.Ev 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
.Nm .
Resource limits and session priority applicable to the original user's
login class (See
.Xr login.conf 5 )
are also normally retained unless the target login has a user ID of 0.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl K
Do not attempt to use Kerberos to authenticate the user.
.It Fl f
If the invoked shell is
.Xr csh 1 ,
this option prevents it from reading the
.Dq Pa .cshrc
file.
.It Fl l
Simulate a full login.
The environment is discarded except for
.Ev HOME ,
.Ev SHELL ,
.Ev PATH ,
.Ev TERM ,
and
.Ev USER .
.Ev HOME
and
.Ev SHELL
are modified as above.
.Ev USER
is set to the target login.
.Ev PATH
is set to
.Dq Pa /bin:/usr/bin .
.Ev 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
.Nm
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.
.It Fl
(no letter) The same as
.Fl l .
.It Fl 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
.Xr getusershell 3 )
and the caller's real uid is
non-zero,
.Nm
will fail.
.It Fl c Ar class
Use the settings of the specified login class.
Only allowed for the super-user.
.El
.Pp
The
.Fl l
(or
.Fl )
and
.Fl m
options are mutually exclusive; the last one specified
overrides any previous ones.
.Pp
If the optional
.Ar args
are provided on the command line, they are passed to the login shell of
the target login.
.Pp
Only users who are a member of group 0 (normally
.Dq wheel )
can
.Nm
to
.Dq root .
\ If group 0 is missing or empty, any user can
.Nm
to
.Dq root .
.Pp
By default (unless the prompt is reset by a startup file) the super-user
prompt is set to
.Dq Sy \&#
to remind one of its awesome power.
.Sh ENVIRONMENT
Environment variables used by
.Nm :
.Bl -tag -width HOME
.It Ev HOME
Default home directory of real user ID unless modified as
specified above.
.It Ev PATH
Default search path of real user ID unless modified as specified above.
.It Ev TERM
Provides terminal type which may be retained for the substituted
user ID.
.It Ev USER
The user ID is always the effective ID (the target user ID) after an
.Nm
unless the user ID is 0 (root).
.El
.Sh FILES
.Bl -tag -width /etc/auth.conf -compact
.It Pa /etc/auth.conf
configure authentication services
.El
.Sh EXAMPLES
.Bl -tag -width 5n -compact
.It Li "su man -c catman"
Runs the command
.Li catman
as user
.Li man ,
assuming man's shell supports the
.Fl c
option.
You will be asked for man's password unless your real UID is 0.
.It Li "su -m man -c catman"
Same as above, but use the shell and environment of the current
user instead of those of man.
This allows commands to be executed as user man even when man's shell is
.Xr nologin 8 .
.It Li "su -mf man -c catman"
Same as above, but do not re-evaluate the current user's
.Pa .cshrc
either.
.It Li "su -mf man -c 'catman /usr/share/man /usr/local/man /usr/X11R6/man'"
Same as above, but the target command consists of more than a
single word and hence is quoted for use with the
.Fl c
option being passed to the shell.  (Most shells expect the argument to
.Fl c
to be a single word).
.It Li "su -mf -c staff man -c 'catman /usr/share/man /usr/local/man /usr/X11R6/man'"
Same as above, but the target command is run with the resource limits of
the login class
.Dq staff .
Note: in this example, the first
.Fl c
option applies to
.Nm
while the second is an argument to the shell being invoked.
.It Li "su -l foo"
Simulate a login for user foo.
.It Li "su - foo"
Same as above.
.It Li "su -  "
Simulate a login for root.
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr kerberos 1 ,
.Xr kinit 1 ,
.Xr login 1 ,
.Xr sh 1 ,
.Xr group 5 ,
.Xr login.conf 5 ,
.Xr passwd 5 ,
.Xr environ 7 ,
.Xr nologin 8
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .