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.\"	@(#)su.1	6.12 (Berkeley) 7/29/91
.\"
.Dd July 29, 1991
.Dt SU 1
.Os
.Sh NAME
.Nm su
.Nd substitute user identity
.Sh SYNOPSIS
.Nm su
.Op Fl Kflm
.Op Ar login
.Sh DESCRIPTION
.Nm Su
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.
.Nm Su
will resort to the local password file to find the password for
.Ar login
if there is a Kerberos error.
If
.Nm 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.
.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 su .
.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.
The invoked shell is the target login's, and
.Nm su
will change directory to the target login's home directory.
.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 su
will fail.
.El
.Pp
The
.Fl l
and
.Fl m
options are mutually exclusive; the last one specified
overrides any previous ones.
.Pp
Only users in group 0 (normally
.Dq wheel )
can
.Nm su
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 SEE ALSO
.Xr csh 1 ,
.Xr login 1 ,
.Xr sh 1 ,
.Xr kinit 1 ,
.Xr kerberos 1 ,
.Xr passwd 5 ,
.Xr group 5 ,
.Xr environ 7
.Sh ENVIRONMENT
Environment variables used by
.Nm su :
.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 su
unless the user ID is 0 (root).
.El
.Sh HISTORY
A
.Nm
command appeared in
.At v7 .
The version desribed
here is an adaptation of the
.Tn MIT
Athena Kerberos command.