linux - How to run a command in a chroot jail not as root and without sudo?

Question

I'm setting up a minimal chroot and want to avoid having sudo or su in it but still run my processes as non-root. This is a bit of a trick as running chroot requiers root. I could write a program that does this that would look something like:

uid = LookupUser(args[username])  // no /etc/passwd in jail
chroot(args[newroot])
cd("/")
setuids(uid)
execve(args[exe:])

Is that my best bet or is there a standard tool that does that for me?

---

I rolled my own here:

Answer 1

If you invoke chroot from root, the chroot option --userspec=USER:GROUP will run the command under the non-root UID/GID.

By the way, the option '--userspec' is first introduced in coreutils-7.5 according to a git repository git://git.sv.gnu.org/coreutils.