login-utils/sulogin.8

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  18 .TH SULOGIN 8 "17 Jan 2006" "" "Linux System Administrator's Manual"
  19 .SH NAME
  20 sulogin \- Single-user login
  21 .SH SYNOPSIS
  22 .B sulogin
  23 [ \fB\-e\fP ]
  24 [ \fB\-p\fP ]
  25 [ \fB\-t\fP \fISECONDS\fP ]
  26 [ \fITTY\fP ]
  27 .SH DESCRIPTION
  28 .I sulogin
  29 is invoked by \fBinit(8)\fP when the system goes into single user mode.
  30 (This is done through an entry in \fIinittab(5)\fP.)
  31 \fBInit\fP also
  32 tries to execute \fIsulogin\fP when
  33 the boot loader (e.g., \fBgrub\fP(8))
  34 passes it the \fB\-b\fP option.
  35 .PP
  36 The user is prompted
  37 .IP "" .5i
  38 Give root password for system maintenance
  39 .br
  40 (or type Control\-D for normal startup):
  41 .PP
  42 \fIsulogin\fP will be connected to the current terminal, or to the
  43 optional device that can be specified on the command line
  44 (typically \fB/dev/console\fP).
  45 .PP
  46 If the \fB\-t\fP option is used then the program only waits
  47 the given number of seconds for user input.
  48 .PP
  49 If the \fB\-p\fP option is used then the single-user shell is invoked
  50 with a \fIdash\fP as the first character in \fIargv[0]\fP.
  51 This causes the shell process to behave as a login shell.
  52 The default is \fInot\fP to do this,
  53 so that the shell will \fInot\fP read \fB/etc/profile\fP
  54 or \fB$HOME/.profile\fP at startup.
  55 .PP
  56 After the user exits the single-user shell,
  57 or presses control\-D at the prompt,
  58 the system will (continue to) boot to the default runlevel.
  59 .SH ENVIRONMENT VARIABLES
  60 \fIsulogin\fP looks for the environment variable \fBSUSHELL\fP or
  61 \fBsushell\fP to determine what shell to start. If the environment variable
  62 is not set, it will try to execute root's shell from /etc/passwd. If that
  63 fails it will fall back to \fB/bin/sh\fP.
  64 .PP
  65 This is very valuable together with the \fB\-b\fP option to init. To boot
  66 the system into single user mode, with the root file system mounted read/write,
  67 using a special "fail safe" shell that is statically linked (this example
  68 is valid for the LILO bootprompt)
  69 .PP
  70 boot: linux \-b rw sushell=/sbin/sash
  71 .SH FALLBACK METHODS
  72 \fIsulogin\fP checks the root password using the standard method (getpwnam)
  73 first.
  74 Then, if the \fB\-e\fP option was specified,
  75 \fIsulogin\fP examines these files directly to find the root password:
  76 .PP
  77 /etc/passwd,
  78 .br
  79 /etc/shadow (if present)
  80 .PP
  81 If they are damaged or nonexistent, sulogin will start a root shell
  82 without asking for a password. Only use the \fB\-e\fP option if you
  83 are sure the console is physically protected against unauthorized access.
  84 .SH AUTHOR
  85 Miquel van Smoorenburg <miquels@cistron.nl>
  86 .SH SEE ALSO
  87 init(8), inittab(5).