function runAsWWW()
{
 try 
 {
  process.setgid('www-data');
  process.setuid('www-data');
 } catch (err) 
 {
  console.error('Cowardly refusal to keep the process alive as root.');
  process.exit(1);
 }
}

[program:yourapp]
command=/home/yourappuser/bin/yourapp # the location of your app
autostart=true
autorestart=true
startretries=10
user=yourappuser # the user your app should run as (i.e. *not* root!)
directory=/srv/www/yourapp.com/ # where your application runs from
environment=APP_SETTINGS="/srv/www/yourapp.com/prod.toml" # environmental variables
redirect_stderr=true
stdout_logfile=/var/log/supervisor/yourapp.log # the name of the log file.
stdout_logfile_maxbytes=50MB
stdout_logfile_backups=10

curr, err := user.Current()
// Check err.
www, err := user.Lookup("www-data")
// Check err.
if *curr != *www {
	panic("Go away!")
}

su www-data -c "myserver"

package main
import (
"flag"
"fmt"
"log"
"net"
"net/http"
"os"
"os/exec"
"os/user"
"strconv"
"syscall"
)
var listenFD = flag.Int("l", 0, "listen pid")
func handler(w http.ResponseWriter, req *http.Request) {
u, err := user.Current()
if err != nil {
log.Println(err)
return
}
fmt.Fprintf(w, "%s\n", u.Name)
}
func lookupUser(username string) (uid, gid int, err error) {
u, err := user.Lookup(username)
if err != nil {
return -1, -1, err
}
uid, err = strconv.Atoi(u.Uid)
if err != nil {
return -1, -1, err
}
gid, err = strconv.Atoi(u.Gid)
if err != nil {
return -1, -1, err
}
return uid, gid, nil
}
// FDListener .
type FDListener struct {
file *os.File
}
// Accept .
func (ln *FDListener) Accept() (net.Conn, error) {
fd, _, err := syscall.Accept(int(*listenFD))
if err != nil {
return nil, err
}
conn, err := net.FileConn(os.NewFile(uintptr(fd), ""))
if err != nil {
return nil, err
}
return conn.(*net.TCPConn), nil
}
// Close .
func (ln *FDListener) Close() error {
return ln.file.Close()
}
// Addr .
func (ln *FDListener) Addr() net.Addr {
return nil
}
func start() error {
u, err := user.Current()
if err != nil {
return err
}
if u.Uid != "0" && *listenFD == 0 {
// we are not root and we have no listen fd. Error.
return fmt.Errorf("need to run as root: %s", u.Uid)
} else if u.Uid == "0" && *listenFD == 0 {
// we are root and we have no listen fd. Do the listen.
l, err := net.Listen("tcp", "0.0.0.0:80")
if err != nil {
return fmt.Errorf("Listen error: %s", err)
}
f, err := l.(*net.TCPListener).File()
if err != nil {
return err
}
uid, gid, err := lookupUser("guillaume")
if err != nil {
return err
}
// First extra file: fd == 3
cmd := exec.Command(os.Args[0], "-l", fmt.Sprint(3))
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
cmd.ExtraFiles = append(cmd.ExtraFiles, f)
cmd.SysProcAttr = &syscall.SysProcAttr{
Credential: &syscall.Credential{
Uid: uint32(uid),
Gid: uint32(gid),
},
}
if err := cmd.Run(); err != nil {
return fmt.Errorf("cmd.Run error: %s", err)
}
return nil
} else if u.Uid != "0" && *listenFD != 0 {
// We are not root and we have a listen fd. Do the accept.
ln := &FDListener{file: os.NewFile(uintptr(*listenFD), "net")}
if err := http.Serve(ln, http.HandlerFunc(handler)); err != nil {
return err
}
}
return fmt.Errorf("setuid fail: %s, %d", u.Uid, *listenFD)
}
func main() {
flag.Parse()
if err := start(); err != nil {
log.Fatal(err)
}
}