reboot system or halt processor
Standard C Library (libc, -lc)
() system call reboots the system.
Only the super-user may reboot a machine on demand. However, a reboot is
invoked automatically in the event of unrecoverable system failures.
argument is a mask of options; the
system call interface allows the following options, defined in the include
to be passed to the new kernel or the new bootstrap and init programs.
- The default, causing the system to reboot in its usual fashion.
- Interpreted by the bootstrap program itself, causing it to prompt on the
console as to what file should be booted. Normally, the system is booted
from the file
where xx is the default disk name,
without prompting for the file name.
- Use the compiled in root device. Normally, the system uses the device from
which it was booted as the root device if possible. (The default behavior
is dependent on the ability of the bootstrap program to determine the
drive from which it was loaded, which is not possible on all
- Dump kernel memory before rebooting; see
savecore(8) for more information.
- The processor is simply halted; no reboot takes place. This option should
be used with caution.
- After halting, the shutdown code will do what it can to turn off the
power. This requires hardware support.
- An option allowing the specification of an init program (see
init(8)) other than
/sbin/init to be run when the system
reboots. This switch is not currently available.
- Load the symbol table and enable a built-in debugger in the system. This
option will have no useful function if the kernel is not configured for
debugging. Several other options have different meaning if combined with
this option, although their use may not be possible via the
reboot() system call. See
ddb(4) for more information.
- Normally, the disks are sync'd (see sync(8))
before the processor is halted or rebooted. This option may be useful if
file system changes have been made manually or if the processor is on
- Instead of rebooting, unmount all filesystems except the one containing
currently-running executable, and mount root filesystem using the same
mechanism which is used during normal boot, based on vfs.root.mountfrom
- Initially mount the root file system read-only. This is currently the
default, and this option has been deprecated.
- Normally, the reboot procedure involves an automatic disk consistency
check and then multi-user operations.
RB_SINGLE prevents this, booting the
system with a single-user shell on the console.
RB_SINGLE is actually interpreted by
the init(8) program in the newly booted
When no options are given (i.e.,
is used), the system is rebooted from file “kernel” in the root
file system of unit 0 of a disk chosen in a processor specific way. An
automatic consistency check of the disks is normally performed (see
If successful, this call never returns. Otherwise, a -1 is returned and an error
is returned in the global variable errno
- The caller is not the super-user.
() system call appeared in