How to get process ID of background process in Linux?

In Linux, there are multiple methods to obtain the process ID (PID) of a background process. Here are some commonly used approaches:

1. jobs command combined with %:

When you launch a background process in the terminal, use the jobs command to view active background jobs in your current session. Each background job has a job number, which you can reference using the % symbol. For example, if you run a process in the background, you can retrieve its PID with the following commands:

bash
$ your_command &
$ jobs -l

The jobs -l command lists all jobs along with their corresponding PIDs.

1. $! variable:

After starting a background process, the shell provides a special variable $! that stores the PID of the most recently launched background process. For example:

bash
$ your_command &
$ echo $!

This command outputs the PID of the background process you just initiated.

1. ps command:

The ps command displays the current system's process status. If you know the process name or other identifying characteristics, you can use ps combined with grep to locate the PID. For example:

bash
$ ps aux | grep 'your_command'

Here, aux is a ps parameter that shows detailed information for all processes, followed by grep to search for a specific process name. In the output, the first column typically represents the PID.

1. pgrep command:

The pgrep command directly finds the PID of a process based on its name or other attributes. Compared to the ps and grep combination, pgrep is more concise:

bash
$ pgrep your_command

This command outputs the PIDs of all processes named your_command.

These are several practical methods for obtaining the PID of a Linux background process. In real-world scenarios, select the most appropriate method based on your specific situation to retrieve the required information.