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Will the AnQiCMS process still exist if it is started without `nohup` and the terminal is closed? Is this related to PID?

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AnQiCMS is a high-performance enterprise-level content management system developed based on the Go language, with its core focusing on providing stable and efficient content management services.It is crucial to ensure that any long-running server-side application, such as AnQiCMS, can continue to run stably after startup, even if the terminal session that started it is closed.About not havingnohupStarting the AnQiCMS process with command assistance, as well as the survival issue of the process after the terminal is closed, which is closely related to the Linux system's process management mechanism and the process identifier (PID).

The association between Linux processes and terminal sessions

In the Linux system, when we start a program through the SSH client or local terminal, the program is usually run as a foreground process of the terminal session.This means it is closely connected to the terminal and is part of the terminal session.Each terminal session has a session leader and one or more process groups, and the process started belongs to a process group of the current terminal session.

This connection is an important manifestation, when the terminal session ends (such as closing the SSH window or exiting the terminal emulator), the operating system will send a specific signal to all processes in the session, namelySIGHUP(Hang Up). The default behavior of this signal is to terminate the process that receives it.Therefore, if the AnQiCMS process is started in the terminal without any special handling, it will receive it when the terminal closesSIGHUPSignal and terminate immediately.

not usenohupStart AnQiCMS: Consequences

To be precise, if there is notnohupStart the AnQiCMS process directly under the command wrapper, and close the current terminal window after the start, then the AnQiCMS process will stop running.This is unacceptable for backend applications like AnQiCMS that require continuous online services, because the website will become inaccessible immediately.

AnQiCMS is designed to provide round-the-clock online content management services for small and medium-sized enterprises and content operation teams, which means it needs to run continuously in the background like a watchdog.The ordinary terminal startup method cannot meet this requirement because once the terminal is closed, the processes associated with the terminal session will receive a termination signal.

nohupthe function

nohupCommand (No Hang Up abbreviation) is designed to solve the above problem. Its main function is to make the process ignoreSIGHUPsignal. When a process passes throughnohupIt will be set not to receive the signal at the end of the terminal session when it startsSIGHUPThus allowing it to continue running in the background after the terminal closes.

Ignoring signals,SIGHUPa signal,nohupWill also redirect the process's standard input (stdin), standard output (stdout), and standard error (stderr). Usually, it redirects the standard output and standard error to a file namednohup.outIn the file (if the file does not exist, it will be created), standard input comes from/dev/nullThe advantage of doing this is that even if the terminal that starts it is closed, the process will not be affected because there is nowhere to output or receive input, thereby completely disconnecting from the terminal.Officially provided by AnQiCMSstart.shis explicitly used in the scriptnohupIt is for this reason to ensure that AnQiCMS can continue to run.

The role of the process ID (PID)

The process identifier (PID) is a unique number assigned by the operating system to each running process.It is like the ID number of a process, used for internal identification and management of processes.When you start AnQiCMS, whether you are carryingnohupStill notnohupIt will also get a PID.

However, the PID itself does not determine the lifecycle of a process. Whether a process survives or not depends more on its association with the terminal session and its response to system signals (such asSIGHUPThe response mechanism ofnohupThe command is to change the process toSIGHUPThe response to the signal (ignoring it), rather than changing how the process gets the PID.

When an AnQiCMS process is terminated due to terminal closure, its PID will be**recycled by the system, become available, and may be assigned to a new process in the future.Therefore, PID is simply an identifier that reflects a process running at a certain point in time, but cannot predict the behavior or lifecycle of the process under specific conditions.

Recommended practices to ensure continuous operation of AnQiCMS

Given the continuous online operation feature of AnQiCMS, simply running the program directly in the terminal is not enough to support the production environment. In addition to usingnohupIn addition to this simple and direct way, more robust and professional production environment deployment usually adopts process guard tools.

For example, it can be configured on a Linux system.systemdThe service manages the AnQiCMS process. Throughsystemd，AnQiCMS can be configured to start automatically when the system boots up, and to restart automatically in the event of a failure, while ensuring it runs in the background as a daemon process, detaching from any user session. Similar tools also includeSupervisorThese tools provide more comprehensive process management, logging, and error recovery mechanisms, which are the**practice**to ensure the long-term stability of AnQiCMS.

Summary

WithoutnohupIn this case, start the AnQiCMS process and close the terminal afterwards, the process will terminate upon receivingSIGHUPa signal.nohupThe function is to make the process ignoreSIGHUPSignal it and redirect its standard I/O so that it can continue to run in the background after the terminal is closed.The process identifier (PID) is a unique identifier for a process, it does not directly determine the survival of the process, but rather the association of the process with the terminal session and the mechanism of responding to signals determines the lifecycle of the process.For server-side applications like AnQiCMS, it is imperative to usenohupOr a more professional process guardian tool to ensure its continuous and stable operation.

Frequently Asked Questions (FAQs)

Q1: How to confirm that the AnQiCMS process is running continuously in the background after it starts?

A1: You can usepsCommand to check if the AnQiCMS process is still running. You can try running it in the Linux or macOS terminal.ps -ef | grep anqicmsIf you see any process entries related to AnQiCMS (especially if you arestart.shRenamed the executable file in the script, please use the corresponding name), it means it is running. In addition, checknohup.outLog file (if usednohupStart), check for any new log output, which can also reflect the active state of the process.

Q2: If you accidentally close the terminal, will the AnQiCMS process really stop?

A2: Yes, if the AnQiCMS process is running withoutnohupor other process guardian tools (such assystemdstarted directly in the terminal, then when you close the terminal, the AnQiCMS process will receiveSIGHUPThe signal will default to stopping the operation. Your website will therefore be inaccessible. This is why the AnQiCMS official providesstart.shThe script will default to usingnohupThe reason for the command, to avoid such unexpected termination.

Q3: BesidesnohupWhat are some methods to ensure that AnQiCMS runs continuously and achieves boot-up?

A3: It is recommended to use a more professional process guardian tool for production environments. On Linux systems,systemdis the mainstream choice, you can create asystemdThe unit file defines the start, stop, and restart behavior of the AnQiCMS process, and configures it to run automatically at system startup. In addition,SupervisorIt is also a popular process management tool that can monitor process status and automatically restart processes in case of crashes, ensuring the continuity of services. These tools provide more thannohupMore powerful management and monitoring features.

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