88 lines
3.2 KiB
Groff
88 lines
3.2 KiB
Groff
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'\" -*- coding: UTF-8 -*-
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.\" Copyright (C) 1998-2006 Miquel van Smoorenburg.
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.\"
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.\" This program is free software; you can redistribute it and/or modify
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.\" it under the terms of the GNU General Public License as published by
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.\" the Free Software Foundation; either version 2 of the License, or
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.\" (at your option) any later version.
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.\"
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.\" This program is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public License
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.\" along with this program; if not, write to the Free Software
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.\" Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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.\"
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.TH SULOGIN 8 "17 Jan 2006" "" "Linux System Administrator's Manual"
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.SH NAME
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sulogin \- Single-user login
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.SH SYNOPSIS
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.B sulogin
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[ \fB\-e\fP ]
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[ \fB\-p\fP ]
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[ \fB\-t\fP \fISECONDS\fP ]
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[ \fITTY\fP ]
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.SH DESCRIPTION
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.I sulogin
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is invoked by \fBinit(8)\fP when the system goes into single user mode.
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(This is done through an entry in \fIinittab(5)\fP.)
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\fBInit\fP also
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tries to execute \fIsulogin\fP when
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the boot loader (e.g., \fBgrub\fP(8))
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passes it the \fB\-b\fP option.
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.PP
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The user is prompted
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.IP "" .5i
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Give root password for system maintenance
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.br
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(or type Control\-D for normal startup):
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.PP
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\fIsulogin\fP will be connected to the current terminal, or to the
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optional device that can be specified on the command line
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(typically \fB/dev/console\fP).
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.PP
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If the \fB\-t\fP option is used then the program only waits
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the given number of seconds for user input.
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.PP
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If the \fB\-p\fP option is used then the single-user shell is invoked
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with a \fIdash\fP as the first character in \fIargv[0]\fP.
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This causes the shell process to behave as a login shell.
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The default is \fInot\fP to do this,
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so that the shell will \fInot\fP read \fB/etc/profile\fP
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or \fB$HOME/.profile\fP at startup.
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.PP
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After the user exits the single-user shell,
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or presses control\-D at the prompt,
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the system will (continue to) boot to the default runlevel.
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.SH ENVIRONMENT VARIABLES
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\fIsulogin\fP looks for the environment variable \fBSUSHELL\fP or
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\fBsushell\fP to determine what shell to start. If the environment variable
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is not set, it will try to execute root's shell from /etc/passwd. If that
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fails it will fall back to \fB/bin/sh\fP.
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.PP
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This is very valuable together with the \fB\-b\fP option to init. To boot
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the system into single user mode, with the root file system mounted read/write,
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using a special "fail safe" shell that is statically linked (this example
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is valid for the LILO bootprompt)
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.PP
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boot: linux \-b rw sushell=/sbin/sash
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.SH FALLBACK METHODS
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\fIsulogin\fP checks the root password using the standard method (getpwnam)
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first.
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Then, if the \fB\-e\fP option was specified,
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\fIsulogin\fP examines these files directly to find the root password:
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.PP
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/etc/passwd,
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.br
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/etc/shadow (if present)
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.PP
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If they are damaged or nonexistent, sulogin will start a root shell
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without asking for a password. Only use the \fB\-e\fP option if you
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are sure the console is physically protected against unauthorized access.
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.SH AUTHOR
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Miquel van Smoorenburg <miquels@cistron.nl>
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.SH SEE ALSO
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init(8), inittab(5).
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