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.\" $Id$
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.Dd March 23, 2004
.Dt SU 1
.Os HEIMDAL
.Sh NAME
.Nm su
.Nd substitute user identity
.Sh SYNOPSIS
.Nm su
.Op Fl K | Fl -no-kerberos
.Op Fl f
.Op Fl l | Fl -full
.Op Fl m
.Oo Fl i Ar instance \*(Ba Xo
.Fl -instance= Ns Ar instance
.Xc
.Oc
.Oo Fl c Ar command \*(Ba Xo
.Fl -command= Ns Ar command
.Xc
.Oc
.Op Ar login Op Ar "shell arguments"
.Sh DESCRIPTION
.Nm su
will use Kerberos authentication provided that an instance for the
user wanting to change effective UID is present in a file named
.Pa .k5login
in the target user id's home directory
.Pp
A special case exists for
.Ql root
where roots
.Pa ~/.k5login
needs to contain a row like:
.Qo
user/root@REALM
.Qc
for su to succed.  
.Pp
In the absence of either an entry for current user in said file or
other problems like missing host/hostname@REALM keys in systems
keytab, or user typing the wrong password, 
.Nm su
will fall back to traditional
.Pa /etc/passwd
authentication.
.Pp
The options are as follows:
.Bl -item -width Ds
.It
.Fl K ,
.Fl -no-kerberos
don't use Kerberos.
.It
.Fl f
don't read .cshrc.
.It
.Fl l ,
.Fl -full
simulate full login.
.It
.Fl m
leave environment unmodified.
.It
.Fl i Ar instance ,
.Fl -instance= Ns Ar instance
root instance to use.
.It
.Fl c Ar command ,
.Fl -command= Ns Ar command
command to execute.
.El
.Pp
.Sh BUGS
Note that on BSD systems, where system 
.Nm su
honors wheel group and denies 
.Nm su
to others, all users may become root if they know the root password,
regardless of wheel membership.