File: sulogin.8

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.TH SULOGIN 8 "04 Nov 2003" "" "Linux System Administrator's Manual"
.SH NAME
sulogin -- Single-user login
.SH SYNOPSIS
.B sulogin
.RB [ " -e " ]
.RB [ " -p " ]
.RB [ " -t timeout " ]
.RB [ " tty-device " ]
.SH DESCRIPTION
.I sulogin
is invoked by \fBinit(8)\fP when the system goes into single user mode
(this is done through an entry in \fIinittab(5)\fP). \fBInit\fP also
tries to execute \fIsulogin\fP when it is passed the \fB-b\fP flag
from the bootmonitor (eg, LILO).
.PP
The user is prompted
.IP "" .5i
Give root password for system maintenance
.br
(or type Control-D for normal startup):
.PP
\fIsulogin\fP will be connected to the current terminal, or to the
optional device that can be specified on the command line
(typically \fB/dev/console\fP).
.PP
If the \fB-p\fP flag was set, the single-user shell will be invoked
with a \fIdash\fP as the first character in \fIargv[0]\fP. That will
cause most shells to behave as a login shell. The default is \fInot\fP
to do this, so that the shell will \fInot\fP read \fB/etc/profile\fP
or \fB$HOME/.profile\fP at startup.
.PP
After the user exits the single-user shell, or presses control-d at the
prompt, the system will (continue to) boot to the default runlevel.
.SH ENVIRONMENT VARIABLES
\fIsulogin\fP looks for the environment variable \fBSUSHELL\fP or
\fBsushell\fP to determine what shell to start. If the environment variable
is not set, it will try to execute root's shell from /etc/passwd. If that
fails it will fall back to \fB/bin/sh\fP.
.PP
This is very valuable together with the \fB-b\fP flag to init. To boot
the system into single user mode, with the root file system mounted read/write,
using a special "failsafe" shell that is statically linked (this example
is valid for the LILO bootprompt)
.PP
boot: linux -b rw sushell=/sbin/sash
.SH FALLBACK METHODS
\fIsulogin\fP checks the root password using the standard method (getpwnam)
first.
Then, if the \fB-e\fP option was specified,
\fIsulogin\fP examines these files directly to find the root password:
.PP
/etc/passwd,
.br
/etc/shadow (if present)
.PP
If they are damaged or non-existant, sulogin will start a root shell
without asking for a password. Only use the \fB-e\fP option if you
are sure the console is physically protected against unauthorized access.
.SH AUTHOR
Miquel van Smoorenburg <miquels@cistron.nl>
.SH SEE ALSO
init(8), inittab(5).