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 flag, 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 flag);
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) are permitted as value for magic2. (The
hexadecimal values of these constants are meaningful.)
The flag argument can have the following values:
(RB_AUTOBOOT, 0x1234567). The message `Restarting
system.' is printed, and a default restart is per
formed immediately. If not preceded by a sync(2),
data will be lost.
(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.
(0x4321fedc; since 2.1.30). The message `Power
down.' is printed, the system is stopped, and all
(0xa1b2c3d4; since 2.1.30). The message `Restart
ing 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.
(RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This
means that the CAD keystroke will immediately cause
the action associated to LINUX_REBOOT_CMD_RESTART.
(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 pro
cess may decide upon a proper action (maybe: kill
all processes, sync, reboot).
Only the super-user may use this function.
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.
On success, zero is returned. On error, -1 is returned,
and errno is set appropriately.
EINVAL Bad magic numbers or flag.
EPERM A non-root user attempts to call reboot.
reboot is Linux specific, and should not be used in pro
grams intended to be portable.
sync(2), bootparam(7), ctrlaltdel(8), halt(8), reboot(8)