PWB1/usr/man/man1/su.1

.th SU I 5/31/77
.sh NAME
su  \*-  become privileged user
.sh SYNOPSIS
.bd su
[ name ]
.sh DESCRIPTION
.it Su
allows one to become the super-user, who has
all sorts of marvelous (and correspondingly dangerous) powers.
In order for \fIsu\fR to do its magic, the user must
supply a password.
If the password is correct, \fIsu\fR
will execute the Shell with the UID set to
that of the super-user.
To restore normal UID privileges,
type an end-of-file to the super-user Shell.
.s3
The password demanded is that of the entry ``root''
in the system's password file.
.s3
To remind the super-user of his responsibilities,
the Shell substitutes `#' for its usual prompt `%'.
The ordinary
user's command path search sequence does not apply to the super-user.
The super-users gets
``/bin'', ``/etc'', and ``/''
instead (no current directory).
.s3
The optional argument allows logging in as
.it name
without logging off as yourself.
That is, you get the powers and privileges, if any, of the user whose
.it login
name is
.it name.
In this case,
.it su
asks for that user's password, rather than the super-user password.
.sh "SEE ALSO"
sh(I), pexec(III)
.sh "BUGS"
Although the super-user has powers far beyond those of mortal users,
the super-user does have one frailty that does not beset other users:
namely, a sensitivity to ``kryptonite'' programs.
As explained in
.it krypton\^\c
(VIII), a ``kryptonite'' program is any one extracted
from a backup tape of the original UNIX system,
which, unfortunately, exploded during its early development.
While exposure to a ``kryptonite'' program can be fatal to a super-user,
it more often causes the super-user
to behave in a strange and irrational fashion,
resulting in unexplained system crashes,
scrambled file systems,
missing files, etc.