runit - experiment with runit and other init schemes

Debian 13.4.0 is a good test bed to experiment with runit and other init schemes on GNU/Linux. The experiments below are reproduced in the Debian test bed on arm64 in qemu (UTM, MacBook M4).

Install Debian 13.4 test bed

Run runit as subinit
Boot Debian test bed with runit
Boot Debian test bed with runit and /run/it filesystem

Run Debian’s systemd init as subinit
Run Debian’s sysv init as subinit
Run an other init as subinit

Install Debian 13.4 test bed

Connect a (serial) operator console.

Make a standard Debian install using debian-13.4.0-arm64-netinst.iso, basically

Enter, Enter, Enter, Enter
Enter, Enter, root, root, user, Enter, user, user, Enter
Enter, Enter, Enter, Enter, Yes
Enter, Enter, Enter, Enter
Enter
Enter
Remove iso
Enter

Prepare the system

apt update
apt install -y build-essential psmisc git

Install the runit programs

git clone -b next https://github.com/g-pape/runit
cd runit
package/compile
package/check
install -m0755 command/* /bin/
mv /bin/runit* /sbin/

Create a minimal runit configuration

mkdir -p /etc/runit
tee /etc/runit/1 <<\EOT && chmod 755 $_
#!/bin/sh
mount -oremount,rw /
EOT
cp -p etc/2 /etc/runit/
tee /etc/runit/3 <<\EOT && chmod 755 $_
#!/bin/sh
sv force-shutdown /service/*
mount -oremount,ro /
EOT
mkdir -p /service

The test bed is ready for experiments now.

Run runit as subinit

Install the Debian test bed, and create a runit sshd service listening on port 2217 to be able to login to the runit subinit

mkdir -p /etc/sv/sshd
tee /etc/sv/sshd/run <<\EOT && chmod 755 $_
#!/bin/sh
exec /usr/sbin/sshd -D -p2217
EOT
touch /etc/sv/sshd/down
ln -s /etc/sv/sshd /service/

Run runit-init with chpst -I to start the runit subinit

chpst -I /sbin/runit-init &

You can now add new services to the runit subinit and experiment with the runit configuration.

To login to the runit subinit, start the runit sshd service

sv start sshd
ssh -luser -p2217 localhost
su -

To stop the runit subinit again, login to the runit subinit, become root, and halt the system

runit-init 0

You can create a Debian systemd service for “chpst -I /sbin/runit-init”, just instead of using runit with current init, and experiment with the differences.

Boot Debian test bed with runit

Install the Debian test bed, and create a getty service for /dev/console

mkdir -p /etc/sv/getty-console
tee /etc/sv/getty-console/run <<\EOT && chmod 755 $_
#!/bin/sh
exec agetty console
EOT
ln -s /etc/sv/getty-console /service/

Reboot with runit-init in place of Debian’s /sbin/init

mv /sbin/init /sbin/init.sysd
ln -s runit-init /sbin/init
reboot

pstree

It should print “runit---runsvdir---runsv---login---bash---pstree”, a minimal runit system with just one service running.

You can now add new services to the runit service supervision and experiment with the runit configuration.

Boot Debian test bed with runit and `/run/it` filesystem

First install the Debian test bed, and boot the Debian test bed with runit.

Using the /run/it filesystem enables runit to maintain all runtime data in that filesystem only, so that it doesn’t require any other writable storage.

The prototype runit-fs program in stage 1 sets up the /run/it filesystem as tmpfs

/run/it size=42mb
/run/it/service -> svdir/default
/run/it/svdir/default/
/run/it/sv/
/run/it/etc/ctrlaltdel
/run/it/etc/nosync
/run/it/etc/reboot
/run/it/etc/stopit
/run/it/log/

And then stores services from the default directory /service/ into /run/it/sv/ and enables them in /run/it/service/.

Finally it can store services from directories found in /etc/runit/runsvdir/ into /run/it/sv/ and add these services directories to /run/it/svdir/.

Create the prototype runit-fs program

tee /sbin/runit-fs <<\EOT && chmod 755 $_
#!/bin/sh
set -e
rc=0
USAGE='runit-fs setup|enable-sv|store-sv|store-svdir dir ...'
usage() { echo usage: $USAGE >&2; exit 100; }
skip() { rc=$(($rc+1)); echo Skipping "$1"; }
setup() {
  mkdir -p -m0755 /run/it
  mount -t tmpfs -omode=0755,size=42m,exec tmpfs /run/it
  for i in etc log svdir/default sv; do mkdir -p -m0755 /run/it/$i; done
  for i in stopit reboot ctrlaltdel nosync; do touch /run/it/etc/$i; done
  ln -s svdir/default /run/it/service
  echo Set up /run/it:
  find /run/it
}
store_sv() {
  test -d "$1" || { skip "$1: not a directory"; return; }
  d=$(cd "$1" && pwd -P); s=${1##*/}
  test ! -e /run/it/sv/"$s" || { skip "/run/it/sv/$s: already exists"; return; }
  mkdir -m0755 /run/it/sv/"$s"; cd /run/it/sv/"$s"; ln -s "$d" .source
  for i in run finish down check; do cp -p "$d"/$i ./ ||:; done 2>/dev/null
  test ! -d "$d"/log || {
    mkdir -m0755 log
    for i in run finish down; do cp -p "$d"/log/$i log/ ||:; done; } 2>/dev/null
  test ! -d "$d"/control || {
    mkdir -m0755 control
    for i in "$d"/control/?; do cp -p "$i" control/ ||:; done; } 2>/dev/null
  echo "Stored $d in /run/it/sv/$s:"
  find /run/it/sv/"$s"
}
enable() {
  test -d /run/it/sv/"$1" || { skip "/run/it/sv/$1: not a directory"; return; }
  test -d /run/it/svdir/"$2" || {
    skip "/run/it/svdir/$2: not a directory"; return; }
  test ! -e /run/it/svdir/"$2"/"$1" || {
    skip "/run/it/svdir/$2/$1: already exists"; return; }
  ln -s /run/it/sv/"$1" /run/it/svdir/"$2"/ || return 0;
  echo "Enabled $1 in /run/it/svdir/$2."
}
enable_sv() {
  store_sv "$1"
  enable "${1##*/}" "$2"
}
store_svdir() {
  test -d "$1" || { skip "$1: not a directory"; return; }
  mkdir -p -m0755 /run/it/svdir/"${1##*/}"
  for i in "$1"/*; do enable_sv "$i" "${1##*/}"; done
  echo "Stored $1 in /run/it/svdir/${1##*/}:"
  find /run/it/svdir/"${1##*/}"
}
diff_sv() {
  test -d /run/it/sv/"$1" || { skip "/run/it/sv/$1: not a directory"; return; }
  test -d /run/it/sv/"$1"/.source || {
    skip "/run/it/sv/$1/.source: not a directory"; return; }
  diff -ur $2 "$(cd /run/it/sv/"$1"/.source && pwd -P)" /run/it/sv/"$1"/ ||:
}
test -n "$2" || usage
case "$1" in
  setup) test "$2" = /run/it || usage; setup ;;
  store-sv) shift; for i in "$@"; do store_sv "${i%/}"; done ;;
  enable-sv) shift; for i in "$@"; do enable_sv "${i%/}" default; done ;;
  store-svdir) shift; for i in "$@"; do store_svdir "${i%/}"; done ;;
  diff-sv) shift; for i in "$@"; do diff_sv "$i"; done ;;
  *) usage ;;
esac
exit $rc
EOT

Replace stage 1 to use the prototype runit-fs program:

tee /etc/runit/1 <<\EOT
#!/bin/sh
runit-fs setup /run/it
runit-fs enable-sv /service/*
EOT

Adjust stage 2 and stage 3 to run runsvdir in /run/it/service instead of /service

sed -i 's} /service} /run/it/service}' /etc/runit/[23]

Reboot into test bed with all runtime data in the /run/it filesystem

init 6

cat /proc/mounts

It should show the /run/it filesystem mounted read-write and / mounted read-only.

Since now /run/it/service is used instead of the default /service directory, set the environment variable SVDIR accordingly

export SVDIR=/run/it/service

To add new services to the runit service supervision and experiment with the runit configuration, remount the root filesystem read-write

mount -oremount,rw /

And don’t forget the additional step to store new services into the /run/it filesystem

runit-fs enable-sv /service/new-service

It should print “Enabled new-service in /run/it/svdir/default.” as last line.

Run Debian’s systemd init as subinit

First install the Debian test bed, and boot the Debian test bed with runit. Optionally boot the Debian test bed with runit and /run/it filesystem to have runit even more step aside.

Make sure the root filesystem is writable

mount -oremount,rw /

Create a service subsystemd

mkdir -p /etc/sv/subsystemd
tee /etc/sv/subsystemd/run <<\EOT && chmod 755 $_
#!/bin/sh
exec chpst -b /sbin/init -vI sh -ec '
umount /dev/pts /dev /sys
export container=
exec /sbin/init.sysd
'
EOT
mkdir -p /etc/sv/subsystemd/control
tee /etc/sv/subsystemd/control/t <<\EOT  && chmod 755 $_
#!/bin/sh
exec kill -SIGRTMIN+3 "$1"
EOT
touch /etc/sv/subsystemd/down
ln -s /etc/sv/subsystemd /service/

When using /run/it for runtime data, store the subsystemd service into that filesystem and adjust the environment, otherwise skip this

runit-fs enable-sv /service/subsystemd
export SVDIR=/run/it/service

Remove Debian’s console getty service to prevent the subsystemd from taking over the console with your login

rm /lib/systemd/system/console-getty.service

Start Debian’s systemd init as subinit

sv once subsystemd

To login to the subsystemd, use Debian’s default sshd service

ssh -luser localhost
su -

To stop it again, do

sv stop subsystemd

It should print “ok: down: subsystemd: 0s”.

Run Debian’s sysv init as subinit

First install the Debian test bed, and boot the Debian test bed with runit.

Connect to the network

mkdir -p /etc/sv/dhcpcd
tee /etc/sv/dhcpcd/run <<\EOT && chmod 755 $_
#!/bin/sh
exec dhcpcd -B
EOT
ln -s /etc/sv/dhcpcd /service/

Prepare Debian’s sysv init

rm -rf /run/systemd/system
apt update
apt -y --purge --allow-remove-essential install sysvinit-core libpam-elogind dbus-x11 systemd-sysv-

And make sure runit-init remains /sbin/init

mv /sbin/init /sbin/init.sysv
ln -s runit-init /sbin/init

Stop the dhcpcd service again and don’t start it automatically

sv stop dhcpcd
touch /etc/sv/dhcpcd/down

Create a service subsysv

mkdir -p /etc/sv/subsysv
tee /etc/sv/subsysv/run <<\EOT && chmod 755 $_
#!/bin/sh
exec chpst -b /sbin/init -I /sbin/init.sysv
EOT
touch /etc/sv/subsysv/down
ln -s /etc/sv/subsysv /service/

Start Debian’s sysv init as subinit

sv once subsysv

Unfortunately this experiment is not that successful as for some reason the attempt to login through Debian’s default sshd service

ssh -luser localhost

prints “Host key verification failed.” and fails.

To stop sysv subinit forcibly, do

sv quit subsysv

The sysv subinit and all its children exit immediately.

Run an other init as subinit

Running other init schemes should be similar to running runit as subinit:

Install the Debian test bed. Optionally boot the Debian test bed with runit and boot the Debian test bed with runit and /run/it filesystem to have runit even more step aside.

Install the other init scheme and create a minimal configuration for it if necessary.

Create a sshd service listening on port 2217 following the other init’s documentation to be able to login to the other subinit.

Install the init program of the other init to /sbin/other-init and run it with chpst -I to start the subinit

install /other/init/program /sbin/other-init
chpst -b /sbin/init -I /sbin/other-init &

You can now add new services to the other subinit.

To login to the other subinit, use the sshd service on port 2217

ssh -luser -p2217 localhost
su -

You should be able to run “chpst -b /sbin/init -I /sbin/other-init” under any init system as a service, similar to running Debian’s systemd as subinit under runit.

Gerrit Pape <pape@smarden.org>

runit - experiment with runit and other init schemes

Install Debian 13.4 test bed

Run runit as subinit

Boot Debian test bed with runit

Boot Debian test bed with runit and /run/it filesystem

Run Debian’s systemd init as subinit

Run Debian’s sysv init as subinit

Run an other init as subinit

Boot Debian test bed with runit and `/run/it` filesystem