Is os.FindProcess Enough to Reliably Verify Process Existence?

Is os.FindProcess sufficient for verifying process existence?

In scenarios where the PID of a process is known, you might wonder if utilizing os.FindProcess alone adequately establishes the process's existence. This article delves into this specific scenario and provides an alternative approach that leverages operating system principles.

os.FindProcess limitations

• os.FindProcess is an initial step in verifying the presence of a process. However, considering only whether it returns an error is insufficient. Exceptions, such as permissions issues, can lead to false negatives.

Alternative approach using kill -s 0

• This method leverages the Unix tradition of sending a signal of 0 to a process. The lack of error indicates the process's existence.
• The following Go function demonstrates this:

import (
    "log"
    "os/exec"
    "strconv"
)

func checkPid(pid int) bool {
    out, err := exec.Command("kill", "-s", "0", strconv.Itoa(pid)).CombinedOutput()
    if err != nil {
        log.Println(err)
    }

    if string(out) == "" {
        return true // pid exist
    }
    return false
}

Improved process existence detection

• Sending a signal of 0 allows not only for existence verification but also insights into the process's ownership.
• For instance, if the kill -s 0 command results in an "operation not permitted" error, it suggests that the process exists but is not owned by the user attempting the verification.

Conclusion

While os.FindProcess provides initial indications of process existence, embracing the traditional Unix approach using kill -s 0 offers more comprehensive verification and insights into process ownership.

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