package main

import (
    "os"
    "time"
    "syscall"
    "fmt"
    "strconv"
)

func printIds(ii int) {
    for {
        fmt.Printf(
            "gorutine %d: uid=%d euid=%d gid=%d egid=%d\n", ii,
            syscall.Getuid(), syscall.Geteuid(),
            syscall.Getgid(), syscall.Getegid(),
        )
        time.Sleep(1e9)
    }
}

func main() {
    if len(os.Args) != 3 {
        fmt.Printf("Usage: %s UID GID\n", os.Args[0])
        os.Exit(1)
    }
    uid, err := strconv.Atoi(os.Args[1])
    if err != nil {
        fmt.Println("Wrong UID:", err)
        os.Exit(1)
    }
    gid, err := strconv.Atoi(os.Args[2])
    if err != nil {
        fmt.Println("Wrong GID:", err)
        os.Exit(1)
    }

    for ii := 1; ii < 10; ii++ {
        go printIds(ii)
        time.Sleep(1e8)
    }

    en := syscall.Setgid(gid)
    if en != 0 {
        fmt.Println("Setgid error:", os.Errno(en))
        os.Exit(1)
    }

    en = syscall.Setuid(uid)
    if en != 0 {
        fmt.Println("Setuid error:", os.Errno(en))
        os.Exit(1)
    }

    printIds(0)
}