sulogin
Single-user login
see also :
init
Synopsis
sulogin
[ -e ] [ -p ] [ -t
SECONDS ] [ TTY ]
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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/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.
see also
init ,
inittab.
author
Miquel van
Smoorenburg <miquels[:at:]cistron[:dot:]nl>