'\" t
.\"     Title: sulogin
.\"    Author: Julianne Frances Haugh
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 11/08/2022
.\"    Manual: System Management Commands
.\"    Source: shadow-utils 4.13
.\"  Language: English
.\"
.TH "SULOGIN" "8" "11/08/2022" "shadow\-utils 4\&.13" "System Management Commands"
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.SH "NAME"
sulogin \- Single\-user login
.SH "SYNTAX"
.PP
\fBsulogin\fR
[\fItty\-device\fR]
.SH "DESCRIPTION"
.PP
The
\fBsulogin\fR
command is invoked by
\fBinit\fR
prior to allowing the user access to the system when in single user mode\&. This feature may only be available on certain systems where
\fBinit\fR
has been modified accordingly, or where the
/etc/inittab
has an entry for a single user login\&.
.PP
The user is prompted
.PP
Type control\-d to proceed with normal startup,
(or give root password for system maintenance):
.PP
Input and output will be performed with the standard file descriptors unless the optional device name argument is provided\&.
.PP
If the user enters the correct root password, a login session is initiated\&. When
\fIEOF\fR
is pressed instead, the system enters multi\-user mode\&.
.PP
After the user exits the single\-user shell, or presses
\fIEOF\fR, the system begins the initialization process required to enter multi\-user mode\&.
.SH "CAVEATS"
.PP
This command can only be used if
\fBinit\fR
has been modified to call
\fBsulogin\fR
instead of
/bin/sh, or if the user has set the
\fIinittab\fR
to support a single user login\&. For example, the line:
.PP
co:s:respawn:/etc/sulogin /dev/console
.PP
should execute the sulogin command in single user mode\&.
.PP
As complete an environment as possible is created\&. However, various devices may be unmounted or uninitialized and many of the user commands may be unavailable or nonfunctional as a result\&.
.SH "CONFIGURATION"
.PP
The following configuration variables in
/etc/login\&.defs
change the behavior of this tool:
.PP
\fBENV_HZ\fR (string)
.RS 4
If set, it will be used to define the HZ environment variable when a user login\&. The value must be preceded by
\fIHZ=\fR\&. A common value on Linux is
\fIHZ=100\fR\&.
.RE
.PP
\fBENV_TZ\fR (string)
.RS 4
If set, it will be used to define the TZ environment variable when a user login\&. The value can be the name of a timezone preceded by
\fITZ=\fR
(for example
\fITZ=CST6CDT\fR), or the full path to the file containing the timezone specification (for example
/etc/tzname)\&.
.sp
If a full path is specified but the file does not exist or cannot be read, the default is to use
\fITZ=CST6CDT\fR\&.
.RE
.SH "FILES"
.PP
/etc/passwd
.RS 4
User account information\&.
.RE
.PP
/etc/shadow
.RS 4
Secure user account information\&.
.RE
.SH "SEE ALSO"
.PP
\fBlogin\fR(1),
\fBsh\fR(1),
\fBinit\fR(8)\&.