shutdown — close down the system
shutdown [ −h | −r ] [−fqs] [ now | hh:ss | +mins ]
[message]
reboot [ −h | −r ] [−fqs] [ now | hh:ss | +mins ]
[message]
fastboot [ −h | −r ] [−fqs] [ now | hh:ss | +mins ]
[message]
halt [ −h | −r ] [−fqs] [ now | hh:ss | +mins ]
[message]
fasthalt [ −h | −r ] [−fqs] [ now | hh:ss | +mins ]
[message]
In general, shutdown prepares the
system for a power down or reboot. A absolute or delta time
can be given, and periodic messages will be sent to all users
warning of the shutdown. If no message is specified on the
command line, shutdown will ask for a
message to be sent, unless the −q option is set.
halt is the same as shutdown -h -q now
fasthalt is the same as shutdown -h -q -f now
reboot is the same as shutdown -r -q now
fastboot is the same as shutdown -r -q -f now
The default delta time, if none is specified, is 2 minutes.
Five minutes before shutdown (or immediately, if shutdown
is less than five minutes away), the /etc/nologin file is created with a message
stating that the system is going down and that logins are no
longer permitted. The login(1) program will not
allow non-superusers to login during this period. A message
will be sent to all users at this time.
When the shutdown time arrives, shutdown notifies all
users, tells init(8) not to spawn more
getty(8)'s, writes the shutdown
time into the /var/log/wtmp
file, kills all other processes on the system, sync(2)'s, unmounts all the
disks, sync(2)'s again, waits for
a second, and then either terminates or reboots the
system.
Prior to unmounting all discs, the SIGQUIT signal is sent to the init process, which will in
turn exec shutdown(8). This allows
for clean unmounting, even if the old inode for the
init process
was unlinked. If the current process ID (PID) equals 1, then
shutdown(8) will pause
forever.
−hHalt the system. Do not reboot. This option is used when powering down the system.
−rReboot the system.
−fFast. When the system is rebooted, the file systems
will not be checked. This is arranged by creating
/fastboot, which
/etc/rc must detect (and
delete).
−qQuiet. This uses a default broadcast message, and does not prompt the user for one.
−sReboot in single user mode. This is arranged by
creating /etc/singleboot,
which simpleinit(8) detects
(and deletes).
The configuration file /etc/shutdown.conf is used to determine the
action to take when halting the machine. The currently
supported file format is extremely primitive. The first line
must contain two strings separated by whitespace. The first
string must be HALT_ACTION and
the second specifies the action you wish to take on halt. The
options allowed are:
This will simply halt the system. This is the default behaviour. Note also that this is the fallback if another option fails.
This will use the kernel power shutdown facility. This is usually only available on machines with Advanced Power Management (APM).
This specifies a command to run to shut down the power. The first character must be a "/". Bear in mind that this command will be run with only the root filesystem mounted (and it will be read-only), and no daemons running.