s6-linux-utils is a set of minimalistic Linux-specific system utilities.
Prefixing the name of this package — and the names of the binaries it provides — with s6- was a naming mistake. It happened in the early days of the s6 project, before it grew and became an ecosystem focused on supervision, service management and init; despite sharing the same author and the same philosophy, and being designed to work with it, s6-linux-utils is not, stricto sensu, part of the s6 ecosystem, and if you arrived here while trying to understand what s6 is, you are on the wrong page. I apologize for the confusion.
s6-linux-utils is free software. It is available under the ISC license.
git clone git://git.skarnet.org/s6-linux-utils
All these commands exit 111 if they encounter a temporary error, and 100 if they encounter a permanent error - such as a misuse. They exit 127 if they're trying to execute into a program and cannot find it, and 126 if they fail to execute into a program for another reason.
There are several good projects aiming to provide a minimal userspace environment for Linux, suitable for embedded systems. Among them, for instance:
Most of the time, these projects aim to implement standard commands in a lightweight way, and they do it well enough. So, although some standard reimplentation already exists in s6-linux-utils and its sibling package s6-portable-utils, it is an explicit non-goal of those packages to duplicate the work of those projects, and no more rewriting of standard commands will occur.