What are the commands for immediate shutdown in Linux?

Linux shutdown command immediately: 1. "shutdown -h now" command, used by root user; 2. "halt" command; 3. "poweroff" command, the effect is equivalent to the "shutdown -h now" command, Not recommended in multi-user mode.

#The operating environment of this tutorial: Red Hat Enterprise Linux 6.1 system, Dell G3 computer.

Shutdown command:

1. shutdown -h now Shut down immediately (for root users)

2. Halt Immediately Shutdown

3. Poweroff Shut down immediately

If you set the shutdown through the shutdown command, you can use the shutdown -c command to cancel the restart

##Command introduction

Some common shutdown/restart commands under Linux include shutdown, halt, reboot, and init. They can all achieve the purpose of restarting the system, but the internal working process of each command is different. , through the introduction of this article, I hope you can use various shutdown commands more flexibly.

1.shutdown

The shutdown command safely shuts down the system. Some users will shut down Linux by directly cutting off the power supply, which is very dangerous. Because Linux is different from Windows, there are many processes running in the background, so forced shutdown may cause the data of the process to be lost, put the system in an unstable state, and even damage the hardware equipment in some systems.

When using the shutdown command before shutting down the system, the system administrator will notify all logged-in users that the system will be shut down. And the login command will be frozen, that is, new users can no longer log in.

It is possible to shut down directly or delay the shutdown for a certain period of time, and it is also possible to restart. This is determined by the fact that all processes will receive signals sent by the system.

This allows programs like vi to have time to save the document currently being edited, and programs such as mail and news can exit normally, etc.

Shutdown performs its job by sending a signal to the init program, asking it to change the runlevel.

Runlevel 0 is used to shut down (halt), runlevel 6 is used to reactivate (reboot) the system, and runlevel 1 is used to put the system into a state where management work can be performed; this is the default , assuming there is no -h or -r parameter to shutdown. To understand what actions were taken during the shutdown (halt) or restart (reboot) process, you can see the runlevels-related information in this file /etc/inittab.

shutdown Parameter description:

　[-t] Tell init how long to shut down before changing to other runlevels.

　[-r] Restart the calculator.

　[-k] does not actually shut down, but only sends a warning signal to each login [login].

　[-h] Turn off the power after shutdown [halt].

　[-n] No need to init, but shut down by yourself. Using this option is discouraged, and the consequences of this option are often not always what you expect.

　[-c] cancel current processCancel the shutdown program currently being executed. So of course this option has no time parameter, but you can enter a message to explain it, and this message will be sent to each user.

　[-f] Ignore fsck when restarting the calculator [reboot].

　[-F] Force fsck when restarting the calculator [reboot].

　[-time] Set the time before shutdown [shutdown].

2.halt----The simplest shutdown command

In fact, halt is to call shutdown -h. When halt is executed, the application process is killed, the sync system call is executed, and the kernel is stopped after the file system write operation is completed.

Parameter description:

　[-n] Prevent sync system calls. It is used after patching the root partition with fsck to prevent the kernel from overwriting the patched one with an old version of the superblock. Super block.

　[-w] is not a real restart or shutdown, it just writes wtmp [/var/log/wtmp] records.

　[-d] Do not write wtmp records [included in option [-n]].

　[-f] Force shutdown or restart without calling shutdown.

　[-i] Before shutting down (or restarting), turn off all network interfaces.

　[-p] This option is the default option. Just call poweroff when shutting down.

3.poweroff command

poweroff means immediate shutdown. The effect is equivalent to shutdown -h now. It is not recommended to use in multi-user mode (Run Level 3).

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