Setting up s6 on Gentoo II

S. Gilles

2017-03-25

As I mentioned, I really like s6. I had some time off, so I decided
to convert my heavy-duty desktop (my lightweight laptop is already
converted) using the steps I followed. Here are some of the caveats
I found with my guide:

 o Make sure your kernel has input modules compiled in. My desktop,
   for example, had usbhid as a module, which made interacting via
   keyboard difficult. I never noticed on my laptop because I don't
   use usb peripherals there.

 o Make sure that your kernel commandline specifies that the root
   partition is rw. This is because of the “ln -sf /proc/mounts
   /etc/mtab” line in /etc/rc.init. I never noticed on my laptop
   because it uses an odd, baked-in bootloader that happens to set
   rw.

   In case you happen to be using the excellent extlinux bootloader,
   my relevant config entry is:

        LABEL kernel-mainline-s6
              MENU LABEL kernel-mainline [s6]
              KERNEL ../kernel-mainline
              APPEND root=/dev/sda3 rw init=/sbin/init.s6

 o Make sure /etc/rc.init is +x! The same goes for /etc/rc.tini,
   but the init is more noticable.

 o My device-ownership target (the thing which set /dev/fb0 to have
   the correct ownership) needed many, many more entries. After
   adding entries for video, audio, tty, etc. I began to realize I
   was doing it completely wrong. Instead, I needed to run ‘udevadm
   trigger’ after udev was up and initialized. This magically lets
   X11 and friends work. I can't seem to figure out exactly when
   this needs to be called, however, so I have a ‘udev-settled’
   target that runs

        #!/bin/execlineb -P
        foreground { udevadm settle }
        foreground { udevadm trigger }
        foreground { udevadm settle }
        foreground { sleep 10 }
        foreground { udevadm trigger }
        foreground { sleep 10 }
        foreground { udevadm trigger }

   That certainly does it, although it makes me want to wash my
   hands.

 o ALSA starts out muted. There's a whole fancy script to save and
   restore volume levels provided by alsa-utils, but I just want
   it on, so my alsa target looks like

        #!/bin/execlineb -P
        exec -c
        redirfd -a 2 /dev/null
        redirfd -a 1 /dev/null
        foreground { amixer -c 1 sset Master Playback 80 }
        foreground { amixer -c 1 sset Master on }

   I think the card is specific to my system.

 o In my previous writeup, I completely forgot to mention the
   /etc/rc.shutdown script. It's rather important (compare /sbin/init
   and rc.init with rc.init and /etc/rc.shutdown). Again, the default
   worked just fine for me. Note that the ‘s6-${1}’ call at the end
   is the s6 equivalent of ‘halt’ or ‘shutdown’ or whatever other
   init systems call the program that contains magic.

        #!/bin/execlineb -S0
        
        foreground { s6-echo "Syncing disks." }
        foreground { s6-sync }
        foreground { s6-echo "Sending all processes the TERM signal." }
        foreground { s6-nuke -th }
        s6-sleep 2
        foreground { s6-echo "Sending all processes the KILL signal." }
        foreground { s6-nuke -k }
        wait { }
        
        foreground { s6-echo "Syncing disks." }
        foreground { s6-sync }
        foreground { s6-echo "Unmounting disks." }
        foreground { mount -o ro,remount / }
        
        # Havoc is played with this, since the kernel is responsible for the devtmpfs
        # foreground { s6-umount -a }
        
        foreground { s6-echo "\nPerforming ${1}.\n" }
        s6-${1} -f

So now my hulking desktop, which used to take a good minute to start
up (can't log in until the local test instance of nginx is fully
initialized!) has a 17 second BIOS-to-X11 time.  That's pretty good.