mirror of https://github.com/mkerrisk/man-pages
254 lines
6.8 KiB
Groff
254 lines
6.8 KiB
Groff
.\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added notes on capability requirements
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.\"
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.TH REBOOT 2 2019-03-06 "Linux" "Linux Programmer's Manual"
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.SH NAME
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reboot \- reboot or enable/disable Ctrl-Alt-Del
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.SH SYNOPSIS
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/* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*
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for the constants and a fourth argument to the call: */
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.PP
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.B #include <unistd.h>
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.br
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.B #include <linux/reboot.h>
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.PP
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.BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg );
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/* Under glibc and most alternative libc's (including uclibc, dietlibc,
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musl and a few others), some of the constants involved have gotten
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symbolic names RB_*, and the library call is a 1-argument
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wrapper around the system call: */
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.PP
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.B #include <unistd.h>
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.br
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.B #include <sys/reboot.h>
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.PP
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.BI "int reboot(int " cmd );
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.SH DESCRIPTION
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The
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.BR reboot ()
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call reboots the system, or enables/disables the reboot keystroke
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(abbreviated CAD, since the default is Ctrl-Alt-Delete;
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it can be changed using
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.BR loadkeys (1)).
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.PP
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This system call fails (with the error
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.BR EINVAL )
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unless
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.I magic
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equals
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.B LINUX_REBOOT_MAGIC1
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(that is, 0xfee1dead) and
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.I magic2
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equals
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.B LINUX_REBOOT_MAGIC2
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(that is, 672274793).
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However, since 2.1.17 also
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.B LINUX_REBOOT_MAGIC2A
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(that is, 85072278)
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and since 2.1.97 also
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.B LINUX_REBOOT_MAGIC2B
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(that is, 369367448)
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and since 2.5.71 also
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.B LINUX_REBOOT_MAGIC2C
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(that is, 537993216)
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are permitted as values for
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.IR magic2 .
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(The hexadecimal values of these constants are meaningful.)
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.PP
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The
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.I cmd
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argument can have the following values:
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.TP
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.B LINUX_REBOOT_CMD_CAD_OFF
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.RB ( RB_DISABLE_CAD ,
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0).
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CAD is disabled.
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This means that the CAD keystroke will cause a
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.B SIGINT
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signal to be
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sent to init (process 1), whereupon this process may decide upon a
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proper action (maybe: kill all processes, sync, reboot).
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.TP
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.B LINUX_REBOOT_CMD_CAD_ON
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.RB ( RB_ENABLE_CAD ,
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0x89abcdef).
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CAD is enabled.
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This means that the CAD keystroke will immediately cause
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the action associated with
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.BR LINUX_REBOOT_CMD_RESTART .
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.TP
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.B LINUX_REBOOT_CMD_HALT
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.RB ( RB_HALT_SYSTEM ,
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0xcdef0123; since Linux 1.1.76).
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The message "System halted." is printed, and the system is halted.
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Control is given to the ROM monitor, if there is one.
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If not preceded by a
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.BR sync (2),
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data will be lost.
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.TP
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.BR LINUX_REBOOT_CMD_KEXEC
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.RB ( RB_KEXEC ,
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0x45584543, since Linux 2.6.13).
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Execute a kernel that has been loaded earlier with
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.BR kexec_load (2).
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This option is available only if the kernel was configured with
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.BR CONFIG_KEXEC .
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.TP
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.B LINUX_REBOOT_CMD_POWER_OFF
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.RB ( RB_POWER_OFF ,
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0x4321fedc; since Linux 2.1.30).
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The message "Power down." is printed, the system is stopped,
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and all power is removed from the system, if possible.
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If not preceded by a
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.BR sync (2),
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data will be lost.
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.TP
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.B LINUX_REBOOT_CMD_RESTART
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.RB ( RB_AUTOBOOT ,
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0x1234567).
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The message "Restarting system." is printed, and a default
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restart is performed immediately.
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If not preceded by a
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.BR sync (2),
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data will be lost.
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.TP
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.B LINUX_REBOOT_CMD_RESTART2
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(0xa1b2c3d4; since Linux 2.1.30).
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The message "Restarting system with command \(aq%s\(aq" is printed,
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and a restart (using the command string given in
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.IR arg )
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is performed immediately.
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If not preceded by a
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.BR sync (2),
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data will be lost.
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.TP
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.BR LINUX_REBOOT_CMD_SW_SUSPEND
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.RB ( RB_SW_SUSPEND ,
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0xd000fce1; since Linux 2.5.18).
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The system is suspended (hibernated) to disk.
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This option is available only if the kernel was configured with
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.BR CONFIG_HIBERNATION .
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.PP
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Only the superuser may call
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.BR reboot ().
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.PP
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The precise effect of the above actions depends on the architecture.
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For the i386 architecture, the additional argument does not do
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anything at present (2.1.122), but the type of reboot can be
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determined by kernel command-line arguments ("reboot=...") to be
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either warm or cold, and either hard or through the BIOS.
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.\"
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.SS Behavior inside PID namespaces
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.\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
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.\" see also commit 923c7538236564c46ee80c253a416705321f13e3
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Since Linux 3.4,
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if
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.BR reboot ()
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is called
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from a PID namespace other than the initial PID namespace
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with one of the
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.I cmd
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values listed below,
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it performs a "reboot" of that namespace:
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the "init" process of the PID namespace is immediately terminated,
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with the effects described in
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.BR pid_namespaces (7).
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.PP
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The values that can be supplied in
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.I cmd
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when calling
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.BR reboot ()
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in this case are as follows:
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.TP
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.BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2
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The "init" process is terminated,
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and
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.BR wait (2)
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in the parent process reports that the child was killed with a
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.B SIGHUP
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signal.
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.TP
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.BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT
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The "init" process is terminated,
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and
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.BR wait (2)
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in the parent process reports that the child was killed with a
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.B SIGINT
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signal.
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.PP
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For the other
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.I cmd
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values,
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.BR reboot ()
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returns \-1 and
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.I errno
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is set to
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.BR EINVAL .
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.SH RETURN VALUE
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For the values of
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.I cmd
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that stop or restart the system,
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a successful call to
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.BR reboot ()
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does not return.
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For the other
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.I cmd
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values, zero is returned on success.
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In all cases, \-1 is returned on failure, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EFAULT
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Problem with getting user-space data under
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.BR LINUX_REBOOT_CMD_RESTART2 .
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.TP
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.B EINVAL
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Bad magic numbers or \fIcmd\fP.
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.TP
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.B EPERM
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The calling process has insufficient privilege to call
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.BR reboot ();
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the caller must have the
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.B CAP_SYS_BOOT
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inside its user namespace.
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.SH CONFORMING TO
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.BR reboot ()
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is Linux-specific,
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and should not be used in programs intended to be portable.
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.SH SEE ALSO
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.BR systemctl (1),
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.BR systemd (1),
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.BR kexec_load (2),
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.BR sync (2),
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.BR bootparam (7),
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.BR capabilities (7),
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.BR ctrlaltdel (8),
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.BR halt (8),
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.BR shutdown (8)
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