.\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
-.\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
+.\" %%%LICENSE_END
+.\"
+.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added notes on capability requirements
.\"
-.TH REBOOT 2 2004-05-27 "Linux 2.6.6" "Linux Programmer's Manual"
+.TH REBOOT 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
reboot \- reboot or enable/disable Ctrl-Alt-Del
.SH SYNOPSIS
-For libc4 and libc5 the library call and the system call are identical,
-and since kernel version 2.1.30 there are symbolic names
-LINUX_REBOOT_* for the constants and a fourth argument to the call:
-.sp
+/* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*
+ for the constants and a fourth argument to the call: */
+.PP
.B #include <unistd.h>
.br
.B #include <linux/reboot.h>
-.sp
-.BI "int reboot(int " magic ", int " magic2 ", int " flag ", void *" arg );
-.sp
-Under glibc some of the constants involved have gotten symbolic names RB_*,
-and the library call is a 1-argument wrapper around the 3-argument
-system call:
-.sp
+.PP
+.BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg );
+
+/* Under glibc and most alternative libc's (including uclibc, dietlibc,
+ musl and a few others), some of the constants involved have gotten
+ symbolic names RB_*, and the library call is a 1-argument
+ wrapper around the system call: */
+.PP
.B #include <unistd.h>
.br
.B #include <sys/reboot.h>
-.sp
-.BI "int reboot(int " flag );
+.PP
+.BI "int reboot(int " cmd );
.SH DESCRIPTION
-The
+The
.BR reboot ()
call reboots the system, or enables/disables the reboot keystroke
(abbreviated CAD, since the default is Ctrl-Alt-Delete;
it can be changed using
.BR loadkeys (1)).
.PP
-This system call will fail (with EINVAL) unless
+This system call fails (with the error
+.BR EINVAL )
+unless
.I magic
-equals LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and
+equals
+.B LINUX_REBOOT_MAGIC1
+(that is, 0xfee1dead) and
.I magic2
-equals LINUX_REBOOT_MAGIC2 (that is, 672274793).
-However, since 2.1.17 also LINUX_REBOOT_MAGIC2A (that is, 85072278)
-and since 2.1.97 also LINUX_REBOOT_MAGIC2B (that is, 369367448)
-and since 2.5.71 also LINUX_REBOOT_MAGIC2C (that is, 537993216)
-are permitted as value for
+equals
+.B LINUX_REBOOT_MAGIC2
+(that is, 672274793).
+However, since 2.1.17 also
+.B LINUX_REBOOT_MAGIC2A
+(that is, 85072278)
+and since 2.1.97 also
+.B LINUX_REBOOT_MAGIC2B
+(that is, 369367448)
+and since 2.5.71 also
+.B LINUX_REBOOT_MAGIC2C
+(that is, 537993216)
+are permitted as values for
.IR magic2 .
(The hexadecimal values of these constants are meaningful.)
+.PP
The
-.I flag
+.I cmd
argument can have the following values:
.TP
-.B LINUX_REBOOT_CMD_RESTART
-(RB_AUTOBOOT, 0x1234567).
-The message `Restarting system.' is printed, and a default
-restart is performed immediately.
-If not preceded by a
-.BR sync (2),
-data will be lost.
+.B LINUX_REBOOT_CMD_CAD_OFF
+.RB ( RB_DISABLE_CAD ,
+0).
+CAD is disabled.
+This means that the CAD keystroke will cause a
+.B SIGINT
+signal to be
+sent to init (process 1), whereupon this process may decide upon a
+proper action (maybe: kill all processes, sync, reboot).
+.TP
+.B LINUX_REBOOT_CMD_CAD_ON
+.RB ( RB_ENABLE_CAD ,
+0x89abcdef).
+CAD is enabled.
+This means that the CAD keystroke will immediately cause
+the action associated with
+.BR LINUX_REBOOT_CMD_RESTART .
.TP
.B LINUX_REBOOT_CMD_HALT
-(RB_HALT_SYSTEM, 0xcdef0123; since 1.1.76).
-The message `System halted.' is printed, and the system is halted.
+.RB ( RB_HALT_SYSTEM ,
+0xcdef0123; since Linux 1.1.76).
+The message "System halted." is printed, and the system is halted.
Control is given to the ROM monitor, if there is one.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
+.BR LINUX_REBOOT_CMD_KEXEC
+.RB ( RB_KEXEC ,
+0x45584543, since Linux 2.6.13).
+Execute a kernel that has been loaded earlier with
+.BR kexec_load (2).
+This option is available only if the kernel was configured with
+.BR CONFIG_KEXEC .
+.TP
.B LINUX_REBOOT_CMD_POWER_OFF
-(0x4321fedc; since 2.1.30).
-The message `Power down.' is printed, the system is stopped,
+.RB ( RB_POWER_OFF ,
+0x4321fedc; since Linux 2.1.30).
+The message "Power down." is printed, the system is stopped,
and all power is removed from the system, if possible.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
+.B LINUX_REBOOT_CMD_RESTART
+.RB ( RB_AUTOBOOT ,
+0x1234567).
+The message "Restarting system." is printed, and a default
+restart is performed immediately.
+If not preceded by a
+.BR sync (2),
+data will be lost.
+.TP
.B LINUX_REBOOT_CMD_RESTART2
-(0xa1b2c3d4; since 2.1.30).
-The message `Restarting system with command '%s'' is printed,
+(0xa1b2c3d4; since Linux 2.1.30).
+The message "Restarting system with command \(aq%s\(aq" is printed,
and a restart (using the command string given in
.IR arg )
is performed immediately.
.BR sync (2),
data will be lost.
.TP
-.B LINUX_REBOOT_CMD_CAD_ON
-(RB_ENABLE_CAD, 0x89abcdef).
-CAD is enabled.
-This means that the CAD keystroke will immediately cause
-the action associated with LINUX_REBOOT_CMD_RESTART.
-.TP
-.B LINUX_REBOOT_CMD_CAD_OFF
-(RB_DISABLE_CAD, 0).
-CAD is disabled.
-This means that the CAD keystroke will cause a SIGINT signal to be
-sent to init (process 1), whereupon this process may decide upon a
-proper action (maybe: kill all processes, sync, reboot).
-.LP
-Only the superuser may use this function.
-.LP
+.BR LINUX_REBOOT_CMD_SW_SUSPEND
+.RB ( RB_SW_SUSPEND ,
+0xd000fce1; since Linux 2.5.18).
+The system is suspended (hibernated) to disk.
+This option is available only if the kernel was configured with
+.BR CONFIG_HIBERNATION .
+.PP
+Only the superuser may call
+.BR reboot ().
+.PP
The precise effect of the above actions depends on the architecture.
For the i386 architecture, the additional argument does not do
anything at present (2.1.122), but the type of reboot can be
-determined by kernel command line arguments (`reboot=...') to be
+determined by kernel command-line arguments ("reboot=...") to be
either warm or cold, and either hard or through the BIOS.
-.SH "RETURN VALUE"
-On success, zero is returned. On error, \-1 is returned, and
+.\"
+.SS Behavior inside PID namespaces
+.\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
+.\" see also commit 923c7538236564c46ee80c253a416705321f13e3
+Since Linux 3.4,
+if
+.BR reboot ()
+is called
+from a PID namespace other than the initial PID namespace
+with one of the
+.I cmd
+values listed below,
+it performs a "reboot" of that namespace:
+the "init" process of the PID namespace is immediately terminated,
+with the effects described in
+.BR pid_namespaces (7).
+.PP
+The values that can be supplied in
+.I cmd
+when calling
+.BR reboot ()
+in this case are as follows:
+.TP
+.BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2
+The "init" process is terminated,
+and
+.BR wait (2)
+in the parent process reports that the child was killed with a
+.B SIGHUP
+signal.
+.TP
+.BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT
+The "init" process is terminated,
+and
+.BR wait (2)
+in the parent process reports that the child was killed with a
+.B SIGINT
+signal.
+.PP
+For the other
+.I cmd
+values,
+.BR reboot ()
+returns \-1 and
+.I errno
+is set to
+.BR EINVAL .
+.SH RETURN VALUE
+For the values of
+.I cmd
+that stop or restart the system,
+a successful call to
+.BR reboot ()
+does not return.
+For the other
+.I cmd
+values, zero is returned on success.
+In all cases, \-1 is returned on failure, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
-Problem with getting userspace data under LINUX_REBOOT_CMD_RESTART2.
+Problem with getting user-space data under
+.BR LINUX_REBOOT_CMD_RESTART2 .
.TP
.B EINVAL
-Bad magic numbers or \fIflag\fP.
+Bad magic numbers or \fIcmd\fP.
.TP
.B EPERM
-The calling process has insufficient privilege to call
+The calling process has insufficient privilege to call
.BR reboot ();
-the
+the caller must have the
.B CAP_SYS_BOOT
-capability is required.
-.SH "CONFORMING TO"
+inside its user namespace.
+.SH CONFORMING TO
.BR reboot ()
-is Linux specific, and should not be used in programs intended to be portable.
-.SH "SEE ALSO"
+is Linux-specific,
+and should not be used in programs intended to be portable.
+.SH SEE ALSO
+.BR systemctl (1),
+.BR systemd (1),
+.BR kexec_load (2),
.BR sync (2),
.BR bootparam (7),
.BR capabilities (7),
.BR ctrlaltdel (8),
.BR halt (8),
-.BR reboot (8)
+.BR shutdown (8)
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