How to Run a Long-Running Process in Go and Detach It from the Parent Process?

Running a Command in Go and Detaching It from the Process

Problem

I need to execute a long-running process in Go, meeting the following requirements:

1. Redirect stdout of the process to a file.
2. Control the user of the process.
3. Ensure the process continues after my program exits.
4. Prevent the process from becoming a zombie when it crashes.
5. Obtain the PID of the running process.

I'm running my program with root permissions and have attempted a solution using exec.Command() and syscall.SysProcAttr, but it fails when I send SIGTERM/SIGKILL to my program, causing the underlying process to crash. I want to run the process as a daemon, separate from my program's control.

Solution

Utilizing an external library, such as github.com/hashicorp/go-reap, is highly recommended as it effectively solves the issue. However, if you prefer a custom implementation, the following approach can be considered:

1. Redirect Standard Output: Use cmd.Stdout = stdLogFile to redirect the process's stdout to a specified file.
2. Control User: Set cmd.SysProcAttr = &syscall.SysProcAttr{Credential: &syscall.Credential{Uid: uid}} to control the user of the process.
3. Detach from Process: Run the command in a separate goroutine using go func() { cmd.Wait() }() to prevent it from becoming a zombie.
4. Obtain PID: Use cmd.Process.Pid to get the PID of the running process.

Note

It's important to acknowledge that it's impossible to completely separate the parent and child processes in terms of process inheritance. All processes must have a parent, and if the parent dies, the child will become an orphan and be adopted by PID 1 (init). In other words, the child cannot have a different parent than the initial process that started it.

To ensure the process continues running after the parent exits, consider using a dedicated process manager like systemd or docker, which can manage orphaned processes and ensure their continued execution. Other potential solutions include writing a custom daemon or using a library like go-daemon to manage the process's lifecycle independently of the parent program.

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