Sl6ckware - Using s6 + s6-rc + s6-linux-init as the init system on Slackware

Note

• This repo is intended to be used on Slackware-current ("current" branch) and Slackware 15.0 ("15.0" branch).
• Before using this repo, read the s6, s6-rc, and s6-linux-init home page first to have a better understanding of what they are and what features or advantages that they provide compared to other init systems. Or for a quick introduction in video format, see this video.

Requirements

1. skalibs
2. execline
3. s6
4. s6-rc
5. s6-linux-init

All of them are available on SBo.

Setup

Compiling a new s6-rc service database

1. Clone this repo.

2. Create a copy of the source directory from this repo and put it somewhere else in your system (e.g. /etc/s6/rc/source).

3. Edit these two files (all paths below are relative to the source directory that you just copied):

   1. bundles/S/contents: this file contains a list of services that are needed to initialize the system, just like the rc.S script. In this file you can (for example) uncomment font service to load a custom screen font for the virtual console (see rc.font/font/up for instructions on how to load your desired custom screen font).
   2. bundles/M/contents: this file contains a list of services that will be started when entering one of the multi user runlevels (runlevel 2, 3, 4, and 5 by default), just like the rc.M script. In this file you can (for example) uncomment cpufreq and bluetooth service to set the default cpu governor and enable bluetooth support, respectively, at boot time.

4. Feel free to edit all other files inside the source directory beside those two files above.

5. Use s6-rc-compile (more details are available in /usr/doc/s6-rc-<version>/doc/s6-rc-compile.html) to compile a new s6-rc service database from your source directory that will be used by s6-rc at runtime to manage services:

   s6-rc-compile /etc/s6/rc/compiled /etc/s6/rc/source/*

   Explanation:

   • /etc/s6/rc/compiled: tell s6-rc-compile to put the compiled database data in /etc/s6/rc/compiled directory (it must not exist beforehand). Of course you can change /etc/s6/rc/compiled to other places that you want.
   • /etc/s6/rc/source/*: tell s6-rc-compile to search for service definition source directories in all subdirectories of /etc/s6/rc/source directory (notice the trailing asterisk). Of course you should change /etc/s6/rc/source to the path of your own copy of source directory.

Setting up s6-linux-init

1. Run the s6-linux-init-maker command (more details are available in /usr/doc/s6-linux-init-<version>/doc/s6-linux-init-maker.html) to create all necessary files that the system needs to be able to properly boot and bring up a full s6 infrastructure. Below is the s6-linux-init-maker invocation that I use for my system (feel free to change them and add any other options that suit your needs):

   s6-linux-init-maker \
       -c /etc/s6/init/current \
       -u adm \
       -G "agetty 38400 tty12 linux" \
       -1 \
       -p "/usr/bin:/usr/sbin:/bin:/sbin" \
       -t 2 \
       -D 4 \
       /etc/s6/init/current

   Explanation:

   • -c /etc/s6/init/current: tell s6-linux-init to look inside /etc/s6/init/current at system startup for all the necessary files it needs in order to boot the system properly. We will reference this directory as basedir.
   • -u adm: the catch-all logger will run as the adm user. The catch-all logger is a service that is started early at boot time to log all system startup and shutdown time messages (except for kernel messages) to the logging directory /run/uncaught-logs (or tmpfsdir/uncaught-logs where tmpfsdir is the argument that was given to the --tmpfsdir= configure option at s6-linux-init build time). This is made possible by using s6-log which takes inputs from stdin and processes them based on the logging script given to it (like adding timestamps, deselect certain lines, etc.). See /usr/doc/s6-<version>/doc/s6-log.html for more details on s6-log.
   • -G "agetty 38400 tty12 linux": start an early getty service by executing the given command line (agetty 38400 tty12 linux). The command line agetty 38400 tty12 linux will start an agetty instance that connects to port /dev/tty12 with baud rate 38400 and TERM=linux.
   • -1: make it so that all the messages that are sent to the catch-all logger are also copied to /dev/console (without timestamps) so those messages will also appear on the computer screen just like Slackware's default init system but better since those messages can still be accessed even after the system has finished booting.
   • -p "/usr/bin:/usr/sbin:/bin:/sbin": set the initial value of the PATH environment variable to /usr/bin:/usr/sbin:/bin:/sbin. Almost all s6-rc service definitions in this repo do not use absolute path when invoking a program so at least these directories should be added to the initial PATH value.
   • -t 2: set the catch-all logger timestamp format to ISO 8601 format.
   • -D 4: set the default runlevel to runlevel 4.
   • /etc/s6/init/current: tell s6-linux-init-maker to put the generated files inside /etc/s6/init/current directory (this directory must not exist beforehand). You can change this argument to other places that you want (e.g. /tmp/init-current) but don't forget to move/copy the generated files back to the declared basedir (/etc/s6/init/current in my case). Use cp -a when copying the generated files since there are fifos, files with precise uid/gid permissions, and files with non-standard access rights, so be sure to copy it verbatim.

2. Edit rc.init, rc.shutdown, and runlevel inside basedir/scripts to incorporate below changes:

   1. rc.shutdown: uncomment exec s6-rc -v2 -bDa change since we're going to use s6-rc as the service manager.
   2. rc.init:
      1. uncomment and change s6-rc-init /run/service to s6-rc-init -c /etc/s6/rc/compiled /run/service. Change /etc/s6/rc/compiled to the path of your new s6-rc service database directory that you have compiled before. Also if you use different tmpfsdir when compiling s6-linux-init, change /run to your tmpfsdir.
      2. uncomment and change exec /etc/s6-linux-init/current/scripts/runlevel "$rl" to s6-rc -v2 -up change "$rl"; exec s6-rc -v1 -bu change gettys. The s6-rc -v2 -up change "$rl" part will bring the system up to the desired runlevel and the exec s6-rc -v1 -bu change gettys part will start all configured gettys (tty1 to tty6 by default). By running s6-rc -v2 -up change "$rl" first and then followed by exec s6-rc -v1 -bu change gettys, the login prompt at tty1 will not be covered by boot time messages that also appear on tty1.
   3. runlevel: uncomment and change exec s6-rc -v2 -up change "$1" to exec s6-rc -v2 -up change gettys "$1". This will make sure the already running gettys are not stopped when changing from one runlevel to another.

3. Edit basedir/bin/init and change s6-linux-init to /sbin/s6-linux-init since the PATH environment variable is undefined at early boot time. This is not necessary if you add /sbin to the default executable search path when compiling skalibs (see its SBo README file for more details on how to do that).

4. Lastly, make a backup copy of /sbin/halt, /sbin/init, /sbin/poweroff, /sbin/reboot, /sbin/shutdown, and /sbin/telinit. Then, copy all scripts inside basedir/bin to /sbin (or alternatively, you can just create symbolic links that point to each scripts inside basedir/bin).

Tips

• The default init system and the s6-based init system can actually coexist by copying/linking the scripts inside basedir/bin to /sbin but using different names (e.g. instead of init, rename it to init.s6). Then, when you want to boot to the s6-based init system, pass init=/sbin/init.s6 (for example) to the kernel as a command line argument. This is mainly useful for testing the s6-based init system before using it as the main init system.
• It's a good idea to use a time-based naming scheme for the compiled s6-rc service database and then create a symbolic link with generic name that points to the service database that you want to use by default at system startup. For example, each time you compile a new database, you run s6-rc-compile compiled-$(date +%y%m%d-%R:%S) source/*. Then, if you want to make it the default service database, make a symbolic link named compiled that points to it. With this approach, you don't have to modify basedir/scripts/rc.init every time you change your default service database.
• If you use symbolic link for the default service database (like above), you probably want to add the -d option to s6-rc-init invocation in basedir/scripts/rc.init. The -d option will tell s6-rc-init to dereference the argument that is given to the -c option (/etc/s6/rc/compiled in my example above) and use that instead. The symbolic link will then not be used by s6-rc and thus can be updated freely without affecting the currently running system. Without the -d option, you have to run s6-rc-update another_compiled_database_absolute_path first before updating the symbolic link.

Quick user guide

• Start a service: s6-rc change service_name
• Stop a service: s6-rc -d change service_name
• Restart a longrun service: s6-svc -r /run/service/service_name
• List all active services: s6-rc -a list
• List all nonactive services: s6-rc -da list
• Switch to another compiled service database: s6-rc-update another_compiled_database_absolute_path

Services not yet converted

Below rc scripts are not yet converted to s6-rc service definition:

• rc.sendmail
• rc.6 (pppd)

Notice of non-affiliation and disclaimer

Sl6ckware is not affiliated, associated, endorsed by, or in any way officially connected with Slackware. The official Slackware website can be found at http://www.slackware.com/.