Huh, looks pretty similar to envuidgid(8) from daemontools. [1]

Another plug for daemontools-encore (last one I promise). The setuidgid(8) program in classic daemontools doesn't set supplementary groups, and a lot of people I know just end up just using sudo in their run files. If you use daemontools-encore though, you can just use `setuidgid -s` instead.

PS. Really, daemontools-encore should imo be called daemontools 1.x, but you know how djb feels about forks of his projects...

[1] http://cr.yp.to/daemontools/envuidgid.html

The problem as per the Phusion blog article is that the runit and possibly daemontools equivalent commands don't set all env vars: HOME, USER, GID & UID, it only calls setgid() & setuid() IIRC. (envuidgid only sets UID and GID[0]) This causes breakage for lots of apps that end up inheriting root's env instead. :(

Here's the go version I wrote, so there's no need for dep on Python/Ruby/etc on the target system:

    setuser USERNAME COMMAND [args...]

    # how to build it
    go get   github.com/steakknife/my_init/setuser
    go build github.com/steakknife/my_init/setuser
    # creates setuser exe here

[0] FR issue submitted as https://github.com/bruceg/daemontools-encore/issues/18

Maintainers either will or won't accept that forks are the sincerest form of flattery.