How to Run External Commands as Another User in Go Without Using su or bash?

Running External Commands as Another User with os/exec

In Go, the os/exec package provides a way to run external commands from a program. However, by default, commands are run with the same user privileges as the program itself.

Running Commands as a Different User (Without su/bash)

To run commands with a different user's privileges without resorting to the su or bash commands, you can use syscall.Credential. Here's an example:

import (
    "os/exec"
    "syscall"
)

func runAsUser(command string, args []string, username string) error {
    // Look up the target user's UID and GID
    u, err := user.Lookup(username)
    if err != nil {
        return err
    }

    uid, err := strconv.Atoi(u.Uid)
    if err != nil {
        return err
    }
    gid, err := strconv.Atoi(u.Gid)
    if err != nil {
        return err
    }

    // Create a command and set its SysProcAttr to run as the specified user
    cmd := exec.Command(command, args...)
    cmd.SysProcAttr = &syscall.SysProcAttr{
        Credential: &syscall.Credential{Uid: uint32(uid), Gid: uint32(gid)},
    }

    // Run the command
    return cmd.Run()
}

Alternative Method Using Setuid (Not Recommended)

While not recommended due to potential security risks, you can also use syscall.Setuid to change the effective user ID of the current process.

import (
    "os"
    "syscall"
)

func setUid(username string) error {
    // Look up the target user's UID
    u, err := user.Lookup(username)
    if err != nil {
        return err
    }

    uid, err := strconv.Atoi(u.Uid)
    if err != nil {
        return err
    }

    // Set the effective user ID to the specified user
    return syscall.Setuid(uid)
}

Note:

• The above examples assume that the current process is running as root with the appropriate su privileges.
• If you need to pass environment variables to the child process, you can set them using Cmd.Env.
• It's crucial to handle any errors that may arise throughout the process.

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