Introduction to commands for server restart in linux

Introduction to commands for server restart in linux

I. Five Linux restart commands

1. shutdown

2. poweroff

3. init

4. reboot

5. halt

Ii. Details of the five restart commands

Shutdown

Reboot

In linux, some common shutdown/restart Commands include shutdown, halt, reboot, and init, which can be used to restart the system. However, the internal working process of each command is different, through the introduction in this article, we hope you can use various shutdown commands more flexibly.

1. shutdown

The shutdown command safely shuts down the system. It is very dangerous for some users to disable linux by directly disconnecting the power supply. Different from windows, linux runs many processes in the background, therefore, force shutdown may lead to data loss in the process, making the system unstable, or even damaging hardware in some systems. When the shutdown command is used before the system is shut down, the system administrator notifies all logged-on users that the system will be shut down. The login command is frozen, meaning that new users cannot log on again. It is possible to directly shut down or wait for a certain period of time to shut down, or restart. This is the signal that all processes will receive from the system [signal 〕

. This allows programs such as vi to have time to store the files being edited, while programs such as mail and news can leave normally.

Shutdown is to send a signal to the init program and ask it to change the runlevel.

Runlevel 0 is used to stop [halt], runlevel 6 is used to reactivate the [reboot] system, and runlevel 1 is used to bring the system into the state where management can be done. This is the preset state. if no-h or-r parameter is set to shutdown. If you want to know what actions are performed during the shutdown (halt) or re-boot (reboot) process, you can view the runlevels related information in the/etc/inittab file.

Shutdown parameter description:

[-T] before changing to another runlevel, tell init how long it will take to shut down.

[-R] restart the calculator.

[-K] does not actually shut down, but only sends a warning signal

Login 〕.

[-H] power off after Shutdown [halt 〕.

[-N] shut down by yourself instead of init. You are not encouraged to use this option, and the consequences of this option are not always what you expected.

[-C] cancel current process cancels the currently running Shutdown program. Therefore, this option certainly does not have a time parameter, but you can enter a message for explanation, and this information will be sent to each user.

[-F] Ignore fsck when restarting calculator [reboot.

[-F] forces The fsck when restarting the calculator [reboot.

[-Time] set the time before shutdown.

2. halt ---- the simplest shutdown command

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

Parameter description:

[-N] prevents the sync system from calling. It is used to fix the root partition with fsck to prevent the kernel from overwriting the repaired super block with the old version of superblock.

[-W] is not a real restart or shutdown, just write

Wtmp (/var/log/wtmp) records.

[-D] Do not write the wtmp record [included in Option [-n 〕.

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

[-I] disable all network interfaces before shutting down (or restarting.

[-P] this option is the default option. It is called poweroff when shutdown.

3. reboot

The reboot process is similar to that of halt, but it causes host restart, while halt is shutdown. Its parameters are similar to those of halt.

4. init

Init is the ancestor of all processes, and its Process number is always 1. Therefore, sending a TERM signal to init will terminate all user processes and daemon processes. Shutdown uses this mechanism. Init defines eight runlevels. init 0 indicates shutdown, and init 1 indicates restart. I will not describe it here for a long article on init. In addition, the telinit command can change the running level of init. For example, telinit-iS can enable the system to enter the single-user mode, and the information and waiting time when shutdown iS not available.