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, 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/console).
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).