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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | SEE ALSO | COLOPHON |
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reboot(2) System Calls Manual reboot(2)
reboot - reboot or enable/disable Ctrl-Alt-Del
Standard C library (libc, -lc)
/* Since Linux 2.1.30 there are symbolic names LINUX_REBOOT_*
for the constants and a fourth argument to the call: */
#include <linux/reboot.h> /* Definition of LINUX_REBOOT_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_reboot, int magic, int magic2, int op, 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: */
#include <sys/reboot.h> /* Definition of RB_* constants */
#include <unistd.h>
int reboot(int op);
The 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 loadkeys(1)).
This system call fails (with the error EINVAL) unless magic
equals LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2
equals LINUX_REBOOT_MAGIC2 (that is, 0x28121969). However, since
Linux 2.1.17 also LINUX_REBOOT_MAGIC2A (that is, 0x05121996) and
since Linux 2.1.97 also LINUX_REBOOT_MAGIC2B (that is,
0x16041998) and since Linux 2.5.71 also LINUX_REBOOT_MAGIC2C
(that is, 0x20112000) are permitted as values for magic2. (The
hexadecimal values of these constants are meaningful.)
The op argument can have the following values:
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).
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.
LINUX_REBOOT_CMD_HALT
(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 sync(2), data will be lost.
LINUX_REBOOT_CMD_KEXEC
(RB_KEXEC, 0x45584543, since Linux 2.6.13). Execute a
kernel that has been loaded earlier with kexec_load(2).
This option is available only if the kernel was configured
with CONFIG_KEXEC.
LINUX_REBOOT_CMD_POWER_OFF
(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 sync(2), data will be lost.
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 sync(2), data will be
lost.
LINUX_REBOOT_CMD_RESTART2
(0xa1b2c3d4; since Linux 2.1.30). The message "Restarting
system with command '%s'" is printed, and a restart (using
the command string given in arg) is performed immediately.
If not preceded by a sync(2), data will be lost.
LINUX_REBOOT_CMD_SW_SUSPEND
(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
CONFIG_HIBERNATION.
Only the superuser may call reboot().
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 either warm or cold, and either hard or through the BIOS.
Behavior inside PID namespaces
Since Linux 3.4, if reboot() is called from a PID namespace other
than the initial PID namespace with one of the op 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 pid_namespaces(7).
The values that can be supplied in op when calling reboot() in
this case are as follows:
LINUX_REBOOT_CMD_RESTART
LINUX_REBOOT_CMD_RESTART2
The "init" process is terminated, and wait(2) in the
parent process reports that the child was killed with a
SIGHUP signal.
LINUX_REBOOT_CMD_POWER_OFF
LINUX_REBOOT_CMD_HALT
The "init" process is terminated, and wait(2) in the
parent process reports that the child was killed with a
SIGINT signal.
For the other op values, reboot() returns -1 and errno is set to
EINVAL.
For the values of op that stop or restart the system, a
successful call to reboot() does not return. For the other op
values, zero is returned on success. In all cases, -1 is
returned on failure, and errno is set to indicate the error.
EFAULT Problem with getting user-space data under
LINUX_REBOOT_CMD_RESTART2.
EINVAL Bad magic numbers or op.
EPERM The calling process has insufficient privilege to call
reboot(); the caller must have the CAP_SYS_BOOT inside its
user namespace.
Linux.
systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7),
capabilities(7), ctrlaltdel(8), halt(8), shutdown(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 reboot(2)
Pages that refer to this page: systemctl(1), kexec_load(2), syscalls(2), org.freedesktop.login1(5), systemd.exec(5), systemd.unit(5), capabilities(7), pid_namespaces(7), systemd-poweroff.service(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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