This is a simple tool that based on gosetuidgid, which supports setting uid(setuid), gid(setgid), and supplementary gid (i.e. sgid, setgroup)

This tool does not handle user to uid map, and you must specify uid/gid in number.

The first GID specified will be the new gid of process

$ gosetuidgid
Usage: ./gosetuidgid user-spec command [args]
   eg: ./gosetuidgid tianon bash
       ./gosetuidgid nobody:root bash -c 'whoami && id'
       ./gosetuidgid 1000:1 id

./gosetuidgid version: 1.1 (go1.3.1 on linux/amd64; gc)

Once the user/group is processed, we switch to that user, then we exec the specified process and gosetuidgid itself is no longer resident or involved in the process lifecycle at all. This avoids all the issues of signal passing and TTY, and punts them to the process invoking gosetuidgid and the process being invoked by gosetuidgid, where they belong.

The main point here is to provide a better setuidgid implementation on Android.

• The setuidgid in busybox cannot handle supplementary gid, but in Android various permission are actually expressed by supplementary groups, such as 3003(inet).
• Unlike Linux, you don't various utils in android, so a static-compiled go setuidgid with such feature will be extremely useful.