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Linux 2.6 - man page for sulogin (linux section 8)

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

       sulogin - Single-user login

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

       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 dis-
       played 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/console).

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

       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.

       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

       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/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.

       Miquel van Smoorenburg <miquels@cistron.nl>

       init(8), inittab(5).

					   17 Jan 2006				       SULOGIN(8)

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