Say goodbye to Linux system shutdown problems and use the shutdown command!

For newbies, shutting down the computer properly in Linux can be a difficult task. Incorrect operations may result in data loss or damage to the file system. However, don't worry, Linux system provides a very practical command-shutdown, which can help you shut down the computer easily and correctly.

1. Function

shutdown command can close all programs and restart or shut down according to the user's needs.

When using the shutdown command, before the system is shut down, all login users can be notified that the system will be shut down. At this time, the login command will be frozen, and new users will no longer be able to log in. This is the recommended safe shutdown method. Before shutting down, all processes will receive the shutdown process signal sent by the shutdown command, and then send a signal to the init program, requiring it to change the runlevel (runlevel).

Linux system has 7 run levels:
Run level 0: The system is in shutdown state. The system default run level cannot be set to 0, otherwise it cannot start normally;
Run level 1: single-user working state, root authority, used for system maintenance, remote login is prohibited;
Runlevel 2: Multi-user state (without NFS);
Run level 3: Complete multi-user state (with NFS), enter the console command line mode after logging in;
Run level 4: System is not used, reserved;
Run level 5: X11 console, enter the graphical GUI mode after logging in;
Run level 6: The system shuts down and restarts normally. The default run level cannot be set to 6, otherwise it cannot start normally.

2.Command format

shutdown [options] [parameters]

3.Option description

-c
 cancel，其他用户可以取消目前正在执行的关机程序，或者Control-C终止shutdown程序
-k
 仅仅向每个登录用户发出警告信息，并不真正关机
-f
 重新启动时不执行fsck文件系统检查命令；
-F
 重新启动时执行fsck文件系统检查命令；
-h
 关机（halt）或关闭电源（power off），至于选择哪一种取决于系统的关机脚本（有時候可以在 BIOS 中更改）
-H
 关机（halt）；
-P
 关机，等价于 poweroff 命令
-n
 不调用 init 程序进行关机，而由 shutdown 自己进行
-r
 重启。等价于 reboot 命令
-t 
 送出警告信息和删除信息之间要延迟多少秒
--help
 显示帮助信息
--version
 显示版本

4.Commonly used examples

(1) Shut down immediately, where now is equivalent to the state of time 0.

shutdown -H now
//或
halt

(2) The system shut down at 20:25 today.

shutdown -H 20:25

(3) The system restarts immediately.

shutdown -r now
//或
reboot

(4) Send the following warning message, and the system will automatically restart after 30 minutes.

shutdown -r +30 'The system will reboot'

(5) Only a warning is issued and the system will not shut down.

shutdown -k now 'This is just a warning message'

(6) Immediately shut down and cut off the power supply.

shutdown -P now
//或
poweroff

(7) Prank, only give a warning, nothing will happen.

shutdown +10 -k '10分钟后关机'

5. Frequently Asked Questions

(1) What are the differences between shutdown -h, shutdown -H and shutdown -P?

shutdown -H is a shutdown operation, which stops the system but does not turn off the power supply. shutdown -P is a power supply operation. shutdown -h selects whether to turn off the power according to the system's default settings. Turning off the power will send an ACPI command to notify the PSU (Power Supply Unit) power supply.

(2) Shutdown default operation enters single-user maintenance mode.

//Enter single-user maintenance mode after ten minutes

shutdown +10

In this article, we introduce the various parameters and usage of the shutdown command in detail. Mastering this knowledge can make you more comfortable shutting down the Linux system and avoid unnecessary troubles and risks. Whether you are a system administrator or an ordinary user, you should master the use of the shutdown command to use the Linux system more efficiently.

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