Analysis of the function and principle of nohup

Analysis of the role and principle of nohup

In Unix and Unix-like operating systems, nohup is a commonly used command, which is used to run commands in the background. Even if the user exits the current session or closes the terminal window, the command remains able to continue execution. In this article, we will analyze the function and principle of the nohup command in detail.

1. The role of nohup

1. Running commands in the background: Through the nohup command, we can let long-running commands continue to execute in the background without the user exiting the terminal session. Influence. This is very useful when long-running tasks are required, such as file transfer, data processing and other operations.
2. Prevent commands from being suspended: Commands executed by some users may be suspended due to restrictions on the terminal session, causing task interruption. Using nohup can avoid this situation and ensure that the task can be completed smoothly.
3. Output redirection: The nohup command can redirect the command output to the specified file, so that you can easily view the results of the command execution.

2. Analysis of the principle of nohup

1. Orphan process: In a Unix system, when the user exits the terminal session, the system will delete the process group associated with the terminal. Sends a SIGHUP signal, which causes all processes running on the terminal to receive the signal and be terminated. The process started using the nohup command will be set as an orphan process and will not be affected by the SIGHUP signal.
2. File descriptor redirection: The nohup command will redirect standard input, standard output, and standard error output to the specified file, which is nohup.out by default. In this way, even if the user exits the terminal session, the output of the command run will continue to be written to the file for easy viewing by the user.
3. Signal processing: The nohup command will also ignore some signals, such as SIGHUP, SIGINT, SIGQUIT, etc., to ensure that the execution of the command will not be affected when the user exits the terminal. At the same time, nohup will set the SIGCHLD signal as the default processing method to prevent the child process from becoming a zombie process.

Through the above analysis, we can understand the function and principle of the nohup command. Using nohup can ensure that our commands can continue to execute in the background, avoid being suspended or terminated, and improve work efficiency and reliability of task completion. When long-running tasks are required, nohup is a very useful tool that deserves our in-depth understanding and application.

The above is the detailed content of Analysis of the function and principle of nohup. For more information, please follow other related articles on the PHP Chinese website!