linux man page for sulogin

SULOGIN(8)						Linux System Administrator's Manual						SULOGIN(8)

NAME
       sulogin - Single-user login

SYNOPSIS
       sulogin [ -e ] [ -p ] [ -t SECONDS ] [ TTY ]

DESCRIPTION
       sulogin	is invoked by init(8) when the system goes into single user mode.  (This is done through an entry in inittab(5).)  Init also tries
       to execute sulogin when the boot loader (e.g., grub(8)) passes it the -b option.

       The user is prompted

	    Give root password for system maintenance
	    (or type Control-D for normal startup):

       If the root account is locked, as is the default on Ubuntu, no password prompt is displayed and sulogin behaves as if the correct  password
       were entered.

       sulogin will be connected to the current terminal, or to the optional device that can be specified on the command line (typically /dev/con-
       sole).

       If the -t option is used then the program only waits the given number of seconds for user input.

       If the -p option is used then the single-user shell is invoked with a dash as the first	character  in  argv[0].   This	causes	the  shell
       process	to  behave  as	a  login  shell.  The default is not to do this, so that the shell will not read /etc/profile or $HOME/.profile at
       startup.

       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.

ENVIRONMENT VARIABLES
       sulogin looks for the environment variable SUSHELL or sushell 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 /bin/sh.

       This  is  very  valuable  together  with the -b option to init. To boot the system into single user mode, with the root file system mounted
       read/write, using a special "fail safe" shell that is statically linked (this example is valid for the LILO bootprompt)

       boot: linux -b rw sushell=/sbin/sash

FALLBACK METHODS
       sulogin checks the root password using the standard method (getpwnam) first.  Then, if the -e option was specified, sulogin examines  these
       files directly to find the root password:

       /etc/passwd,
       /etc/shadow (if present)

       If  they  are damaged or nonexistent, sulogin will start a root shell without asking for a password. Only use the -e option if you are sure
       the console is physically protected against unauthorized access.

AUTHOR
       Miquel van Smoorenburg <miquels@cistron.nl>

SEE ALSO
       init(8), inittab(5).

								    17 Jan 2006 							SULOGIN(8)