CentOS command learning Summary: shutdown

CentOS command learning Summary: shutdown

Command introduction:

This command can be safely disabled or restarted. The shutdown command can not only shut down the system, but also restart the Linux system.

Command syntax:

/Sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message]

Command parameters:

Parameters

Long Parameter

Description

-

Use/etc/shutdown. allow.

-C

Shutdown interrupted: when the "shutdown-h" command is executed, you only need to press the + key to interrupt the shutdown command.

-F

Disk detection is not performed during restart (fsck)

-F

Disk detection during reboot (fsck)

-H

Power off

-K

Simulate Shutdown (not true shutdown), just send a warning message to the publisher!

-N

Force Shutdown without calling the init process

-R

Shut down the system and restart, similar to Windows restart

-T

Delayed Shutdown Time

-W

Only perform tests. If you do not restart the system, the system only writes the restarted data to the wtmp record file in the/var/log directory.

-- Help

Show command online help

Example:

1: view the help information of the reboot command

[Root @ db-server ~] # Shutdown -- help
Shutdown: invalid option ---
Usage: shutdown [-akrhHPfnc] [-t secs] time [warning message]
-A: use/etc/shutdown. allow
-K: don't really shutdown, only warn.
-R: reboot after shutdown.
-H: halt after shutdown.
-P: halt action is to turn off power.
-H: halt action is to just halt.
-F: do a 'save' reboot (skip fsck ).
-F: Force fsck on reboot.
-N: do not go through "init" but go down real fast.
-C: cancel a running shutdown.
-T secs: delay between warning and kill signal.
** The "time" argument is mandatory! (Try "now ")**
[Root @ db-server ~] #

[root@db-server ~]# man shutdown

SHUTDOWN (8) Linux System Administrator Manual SHUTDOWN (8)

NAME

 shutdown - bring the system down

SYNOPSIS

 /sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message]

DESCRIPTION

 shutdown brings the system down in a secure way. All logged-in users are notified that the system is going

 down, and login(1) is blocked. It is possible to shut the system down immediately or after a specified delay.

 All processes are first notified that the system is going down by the signal SIGTERM. This gives programs like

 vi(1) the time to save the file being edited, mail and news processing programs a chance to exit cleanly, etc.

 shutdown does its job by signalling the init process, asking it to change the runlevel. Runlevel 0 is used to

 halt the system, runlevel 6 is used to reboot the system, and runlevel 1 is used to put to system into a state

 where administrative tasks can be performed; this is the defaultif neither the -h or -r flag is given to shut-

 down. To see which actions are taken on halt or reboot see the appropriate entries for these runlevels in the

 file /etc/inittab.

OPTIONS

 -a Use /etc/shutdown.allow.

 -t sec Tell init(8) to wait sec seconds between sending processes the warning and the kill signal, before

 changing to another runlevel.

-K Don't parse into really shutdown; only send the warning messages to everybody.

 -r Reboot after shutdown.

 -h Halt or poweroff after shutdown.

 -H Halt action is to halt or drop into boot monitor on systems that support it.

 -P Halt action is to turn off the power.

-N [DEPRECATED] Don't parse call init (8) to do the shutdown but do it ourself. The use of this option is dis-

Couraged, and its results are not always what you have before CT.

 -f Skip fsck on reboot.

 -F Force fsck on reboot.

 -c Cancel an already running shutdown. With this option it is of course not possible to give the time argu-

 ment, but you can enter a explanatory message on the command line that will be sent to all users.

 time When to shutdown.

 warning-message

 Message to send to all users.

 The time argument can have different formats. First, it can be an absolute time in the format hh:mm, in which

 hh is the hour (1 or 2 digits) and mm is the minute of the hour (in two digits). Second, it can be in the for-

 mat +m, in which m is the number of minutes to wait. The word now is an alias for +0.

 If shutdown is called with a delay, it creates the advisory file /etc/nologin which causes programs such as

 login(1) to not allow new user logins. Shutdown removes this file if it is stopped before it can signal init

 (i.e. it is cancelled or something goes wrong). It also removes it before calling init to change the runlevel.

The-f flag means too many eboot fast fail? This only creates an advisory file/fastboot which can be tested by the sys-

 tem when it comes up again. The boot rc file can test if this file is present, and decide not to run fsck(1)

 since the system has been shut down in the proper way. After that, the boot process should remove /fastboot.

The-F flag means too large orce fsck? This only creates an advisory file/forcefsck which can be tested by the sys-

 tem when it comes up again. The boot rc file can test if this file is present, and decide to run fsck(1) with

A special regression orce execution? Flag so that even properly unmounted filesystems get checked. After that, the boot process

 should remove /forcefsck.

 The -n flag causes shutdown not to call init, but to kill all running processes itself. shutdown will then

 turn off quota, accounting, and swapping and unmount all filesystems.

ACCESS CONTROL

 shutdown can be called from init(8) when the magic keys CTRL-ALT-DEL are pressed, by creating an appropriate

 entry in /etc/inittab. This means that everyone who has physical access to the console keyboard can shut the

 system down. To prevent this, shutdown can check to see if an authorized user is logged in on one of the vir-

 tual consoles. If shutdown is called with the -a argument (add this to the invocation of shutdown in /etc/init-

 tab), it checks to see if the file /etc/shutdown.allow is present. It then compares the login names in that

 file with the list of people that are logged in on a virtual console (from /var/run/utmp). Only if one of those

 authorized users or root is logged in, it will proceed. Otherwise it will write the message

 shutdown: no authorized users logged in

 to the (physical) system console. The format of /etc/shutdown.allow is one user name per line. Empty lines and

 comment lines (prefixed by a #) are allowed. Currently there is a limit of 32 users in this file.

 Note that if /etc/shutdown.allow is not present, the -a argument is ignored.

HALT OR POWEROFF

 The -H option just sets the init environment variable INIT_HALT to HALT, and the -P option just sets that vari-

 able to POWEROFF. The shutdown script that calls halt(8) as the last thing in the shutdown sequence should

 check these environment variables and call halt(8) with the right options for these options to actually have

 any effect. Debian 3.1 (sarge) supports this.

FILES

 /fastboot

 /etc/inittab

 /etc/init.d/halt

 /etc/init.d/reboot

 /etc/shutdown.allow

NOTES

 A lot of users forget to give the time argument and are then puzzled by the error message shutdown produces.

 The time argument is mandatory; in 90 percent of all cases this argument will be the word now.

 Init can only capture CTRL-ALT-DEL and start shutdown in console mode. If the system is running the X window

 System, the X server processes all key strokes. Some X11 environments make it possible to capture CTRL-ALT-DEL,

 but what exactly is done with that event depends on that environment.

Shutdown wasn has been designed to be run setuid./etc/shutdown. allow is not used to find out who is executing shut-

 down, it ONLY checks who is currently logged in on (one of the) console(s).

AUTHOR

 Miquel van Smoorenburg, miquels@cistron.nl

SEE ALSO

 fsck(8), init(8), halt(8), poweroff(8), reboot(8)

 November 12, 2003 SHUTDOWN(8)

(END) 

2: immediately shut down the Linux system, where now is equivalent to the time 0

[root@db-server ~]# shutdown -h now

Broadcast message from root (pts/1) (Sat Jan 10 18:51:34 2015):

The system is going down for system halt NOW!

3: The system restarts two minutes later. + m indicates that the system is shut down or started up several minutes later.

[root@db-server ~]# shutdown -r +2

Broadcast message from root (pts/2) (Sat Jan 10 19:56:00 2015):

The system is going DOWN for reboot in 2 minutes!

4: set the system to shut down at that time

[root@db-server ~]# shutdown -h 12:30

Or

[root@db-server ~]# shutdown -h 12:30 &

[1] 4578

It is best to use the command & shut down Command for background processing. Other operations are not affected.

Set how long the shutdown command will be executed. The time parameter can be hh: mm or + m. Hh: mm indicates the number of minutes when the shutdown command is executed. For example, "shutdown" indicates that shutdown will be executed. + m indicates that shutdown will be executed in m minutes. A special usage is to use now to execute shutdown immediately. it is worth noting that this part of the parameter cannot be omitted. In addition, note that if shutdown-h is executed, shutdown will be shut down the next day.

5: Pull the message from the previous shutdown command

Run the following command to shut down Linux at, as shown in the following figure. However, if this time point is not suitable, use CTRL + C to cancel it.

[Root @ db-server ~] # Shutdown-h 12: 30

Shutdown canceled.

[Root @ db-server ~] #

You can also execute the following command in another command window:

[Root @ db-server ~] # Shutdown-c

6. send information to all login users

[root@db-server ~]# shutdown -k "now"

Broadcast message from root (pts/2) (Sat Jan 10 20:09:14 2015):

The system is going down to maintenance mode NOW!

Shutdown cancelled.

In addition, the following information will be received in the logon session window:

[root@db-server ~]# 

[root@db-server ~]# 

Broadcast message from root (pts/2) (Sat Jan 10 20:11:34 2015):

The system is going down to maintenance mode NOW!

The following syntax is generally used:

[root@db-server ~]# shutdown -k now "The Server will shutdown now"

Broadcast message from root (pts/1) (Sat Jan 10 20:14:54 2015):

The Server will shutdown now 

The system is going down to maintenance mode NOW!

Shutdown cancelled.

7: no disk detection during restart

[root@db-server ~]# shutdown -fr now

Broadcast message from root (pts/1) (Sat Jan 10 20:23:59 2015):

The system is going down for reboot NOW!

8: How many seconds will the system be shut down and a prompt message be sent to the user?

[root@db-server ~]# shutdown -t 10 -h now "System will shutdown 10 sencond later"

Broadcast message from root (pts/1) (Sat Jan 10 20:33:36 2015):

System will shutdown 10 sencond later