What is the role of `nohup` and `&` in the background running of the process in the AnQiCMS startup script?

As a website operator who has been deeply involved in AnQi CMS for many years, I am well aware of the importance of every detail for the stable operation of the website, especially in terms of process management on the server side, which is of paramount importance. Today, let's delve into the startup script of AnQiCMS.nohupand&What roles do these seemingly simple symbols play, and how do they ensure the continuous online operation of our website?

The foundation for ensuring that AnQiCMS stays online.

When discussing running a web service like AnQiCMS on a Linux server, a core requirement is to ensure that it can run continuously and stably without being affected by our terminal sessions.Imagine you connect to the server via SSH and execute the startup command for AnQiCMS. If you simply press Enter, once you close the SSH terminal, the AnQiCMS process is likely to terminate as well.This is clearly not what we want to see, because it means the website will go offline immediately.In order to avoid this situation,nohupand&Has become an indispensable tool for us.

&: Allows commands to run in the background.

First, let's get to know&Symbol. In the Linux command line, when you add it at the end of a command,&It is used to run the command in the background of the current terminal.This means you can immediately get the command line prompt, continue entering other commands without waiting for the previous command to finish.For AnQiCMS, if we directly executeanqicms &The system will try to start the AnQiCMS service in the background.

Although&It allows commands to run in the background, freeing up our terminal, but it has an important limitation: the background process is still a child process of the current terminal session. When the SSH session is closed, the system sends a signal to all processes associated with that session.SIGHUP(Disconnect) signal. By default, receivingSIGHUPthe process of the signal will terminate. This means that only using&Cannot guarantee that AnQiCMS will continue to run after the terminal is closed, the website still has the risk of going offline.

nohup: The guardian against hang-up signals

To overcome&Limitations of the local limitations,nohupThe command was born.nohupIts full name is "no hang up", which means that its main function is to make the subsequent commands ignoreSIGHUPthe signal. ThroughnohupThe command will not receive signals even if its parent process (such as our SSH terminal) exits.SIGHUPand terminate so that it can run continuously.

Furthermore,nohupWhen executing the command, the standard output and standard error will be automatically redirected tonohup.outIn the file (if no other file is specified), this is done to prevent the process from attempting to write to standard output or standard error when there is no associated terminal.}This provides convenience for us to view the AnQiCMS runtime logs and potential errors later.

Combination拳:nohup command &of powerful functions

tonohupand&Used together, that isnohup command &This is the most commonly used method to start background services in our production environment. The advantages of this combination are:

• Process persistence:nohupEnsure that the AnQiCMS process can withstandSIGHUPThe signal runs continuously even if the terminal session is closed.
• Terminal liberation:&The command goes into the background immediately, allowing the operator to continue using the current terminal to perform other tasks.
• Log recording:nohupThe default behavior is to redirect the output to a file, which is crucial for the operation monitoring and troubleshooting of AnQiCMS.

in AnQiCMS'sstart.shIn the startup script, we can see the typical application of this combination:

nohup $BINPATH/$BINNAME >> $BINPATH/running.log 2>&1 &

Let's break down this command:

• nohup: Make sure the main program of AnQiCMS ($BINPATH/$BINNAME) ignores the hang-up signal.
• $BINPATH/$BINNAMEThis is a variable pointing to the AnQiCMS executable file.
• >> $BINPATH/running.logAppend all standard outputs of the AnQiCMS program (such as normal running information) to$BINPATH/running.logthe file.>>Indicates appending to avoid overwriting previous logs.
• 2>&1: This is an important redirection operation.2Represents standard error output,1Represents standard output.2>&1The meaning is to redirect the standard error output to the same place as the standard output. This way, whether it is the normal operation log of AnQiCMS or possible error messages, they will all be recorded together.running.logIn the file, making it easy for us to view and analyze collectively.
• &: Finally, this symbol will run the entirenohupcommand itself in the background, so thatstart.shAfter the script is executed, it can immediately return to the command line prompt.

Bynohupand&The combination, AnQiCMS can run as an independent background process stably, and its output information is properly recorded without being affected by the terminal disconnection.This is of decisive significance for ensuring the uninterrupted 7x24-hour service of the website, improving user experience, and the efficient management of our operations staff.

Frequently Asked Questions

After AnQiCMS runs in the background, how can I confirm that it is really running?

You can useps -ef | grep anqicmsThe command to view all running processes. If AnQiCMS is running, you will see the output containinganqicmsprocess information with the keyword, where there is usually a process bynohupStarted.

How should I stop the AnQiCMS service?

There is usually a script provided in the AnQiCMS installation directorystop.shscript that will search foranqicmsProcess sends a termination signal. If you need to stop manually, first useps -ef | grep anqicmsFind the PID (Process ID) of the AnQiCMS process, then usekill -9 [PID]command to forcibly terminate the process.

If I forget to usenohupor&What will happen when AnQiCMS is started?

If only startanqicmsAnd without any decoration, AnQiCMS will run as a foreground process, occupying your terminal until you manually stop or close the terminal. If only usinganqicms &, AnQiCMS will run in the background, but once you close the SSH session, the AnQiCMS process is likely to receiveSIGHUPThe signal was terminated, resulting in the website going offline. Therefore, it is imperative to use it in production environments.nohup ... &combination.