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reboot - reboot or enable/disable Ctrl-Alt-Del
/* 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: */
int reboot(int magic, int magic2, int cmd, void *arg);
/* 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: */
int reboot(int cmd);
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 will fail (with EINVAL) unless magic equals
LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and 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
magic2. (The hexadecimal values of these constants are meaningful.)
The cmd argument can have the following values:
(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).
(RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This means that
the CAD keystroke will immediately cause the action associated
(RB_HALT_SYSTEM, 0xcdef0123; since 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 (since Linux 2.6.13)
Execute a kernel that has been loaded earlier with
kexec_load(2). This option is only available if the kernel was
configured with CONFIG_KEXEC.
(0x4321fedc; since 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.
(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.
(0xa1b2c3d4; since 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.
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.
For the values of cmd that stop or restart the system, a successful
call to reboot() does not return. For the other cmd values, zero is
returned on success. In all cases, -1 is returned on failure, and
errno is set appropriately.
EFAULT Problem with getting userspace data under
EINVAL Bad magic numbers or cmd.
EPERM The calling process has insufficient privilege to call reboot();
the CAP_SYS_BOOT capability is required.
reboot() is Linux-specific, and should not be used in programs intended
to be portable.
sync(2), bootparam(7), capabilities(7), ctrlaltdel(8), halt(8),
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