[Announce] s6.rc: a distribution-friendly init/rc framework

["Casper Ti. Vector" <caspervector@gmail.com>]

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s6.rc [1] is an attempt to bridge the gap between the elegant foundation
provided by s6/s6-rc and an init/rc system that implements the main
functionalities beneficial for distributions.  s6.rc features a
preprocessor that generates source directories for use with s6-rc from
given templates.  The preprocessing procedure is composed of multiple
tiny passes, which makes the preprocessor not only clean and powerful,
but also extensible.  Using the preprocessor, s6.rc supports instanced
supervision, optional dependencies, in-place `up'/`down' scripts,
automatic connection between services and loggers, as well as
package-specific passes that can be plugged into the preprocessing
phase.

[1] <https://gitlab.com/CasperVector/s6rc-dotrc>.

The init part of s6.rc is, in many aspects, similar to what one would
expect from s6-linux-init.  The stage 1/2/3 scripts shipped with s6.rc
additionally support features like setting the time using hwclock(8) or
other means before exec()ing `s6-svscan' (cf. the documentation for the
rationale), duplicating (while writing to `/run/uncaught-logs') verbose
`s6-rc' output to `/dev/console', automatic reboot under certain
circumstances (eg. when required by fsck(8)), and automatically saving
`/run/uncaught-logs/current' on shutdown.

The attached tarball is an s6.rc-based example setup tailored for Alpine
3.7.x; a VM image of the setup is available at [2].  Due to a lack of
expressiveness in execline, most scripts in s6.rc are written for the
Byron Rakitzis implementation [3] of the rc(1) shell from Plan 9, and
static-linked binaries for x86 [4] and x86_64 [5] are available for
download.  See the attachments for SHA512 checksums (signed using my
OpenPGP public key) of the tarball, the VM image and the rc(1) binaries.

[2] <https://drive.google.com/open?id=1x3BM11C5clU9DTGbgsBmaBssMUtMUItM>.
[3] <https://github.com/rakitzis/rc>.
[4] <https://drive.google.com/open?id=0B3FGvKEMCkmXLUJDQll2VFNsNVE>.
[5] <https://drive.google.com/open?id=0B3FGvKEMCkmXMm9odWhVdVR1Znc>.

Of course, this is just the beginning; a lot of work has to be done:

* Although s6.rc can be easily configured to be rock solid, it is fairly
  fragile to PEBKACs: eg. if you accidentally delete `s6.rc' and then
  reboot the system, the system can get into quite serious troubles.
  Sprinkling related scripts with a lot of "if something is unset then
  default to blah" clauses can avoid the problem, but seems to make
  the code bloated.  Is there a better solution?

* Many more service definitions and ancillary files are necessary for
  s6.rc to be useful for the general public instead of just a few users,
  so any contribution / suggestion is welcome.  BTW, I do not consider
  myself to be a really good documentation writer, so please tell me if
  you have a good idea on improving the s6.rc documentation.

* In principle, it is possible to implement something like Gentoo's
  netifrc [6] using s6.rc's preprocessor, and I believe it would be much
  cleaner than netifrc.  However, since I am not exactly familiar with
  the networking stuffs, perhaps it had better be done by someone else.

[6] <https://wiki.gentoo.org/wiki/Netifrc>.

-- 
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