Runit tools in busybox - up to the task?

Let's test busybox's runit applets in a hypothetical ;) scenario
when someone needs to stop running, say, systemd on, say, a Fedora machine.

No doubt this will expose various shortcomings.

Started with the machine configured and running under systemd.
Machine has xfce4 desktop environment installed.

Created /var/service and copied busybox/examples/var_service/* there.

Renamed/copied getty_tty1 to getty_tty9/10/11/12 (these consoles are not used
by existing setup).

Deleted dhcpd_if, ftpd, httpd, inetd, nmeter, tftpd (hmm, this needs a way
to store inactive services somewhere in a separate directory).

Adjusted fw/run (need more configurable way to do it; lacks a way to specify
more than one "external" (firewalled) interface).

Renamed/copied dhcp_if, dhcp_if_pinger, ifplugd_if each to a pair
of services for eth0 and wlan0.
Renamed supplicant_if only for wlan0.
Renamed zcip_if only for eth0 (how exactly zeroconf supposed to coexist
on more than one iface? They would all have 169.254/16 subnet - ?!).

Created a user to save all logs under:
	groupadd -f --system logger
	useradd --system -g logger -d /tmp -s /bin/false logger

Created /var/service/start:

	#!/bin/sh
	dir=/var/service
	export PATH=/sbin:/bin:/usr/sbin:/usr/bin
	exec </dev/null
	exec >/dev/null 2>&1
	umask 022
	cd "$dir" || exit $?
	exec env - PATH="$PATH" runsvdir -P "$dir"

Created /etc/systemd/system/var.service:

	[Unit]
	Description=/var/service support
	[Service]
	ExecStart=/var/service/start

Added symlink: /etc/systemd/system/multi-user.target.wants/var.service ->
-> /etc/systemd/system/var.service

Deinstalled NetworkManager.

Rebooted and tested that services from /var/service do start, and nicely
coexist with the rest of the system.

Tested network (DHCP, zeroconf) and local DNS caching to work.

Now we will pry off X startup from systemd.

Changed /etc/systemd/system/default.target symlink to point to
/lib/systemd/system/multi-user.target instead of a GUI link.
Reboot. Now the system should start with Linux text VT's.

Created /var/service/lightdm_tty8 service. For user's convenience,
it's activated by pressing Enter at a chosen tty.
This is the run file:

	#!/bin/sh
	tty="/dev/${PWD##*/lightdm_}"
	need "$tty"
	exec <"$tty"
	exec >"$tty" 2>&1
	# If udevd is not up, X may fail to find any input devices. Wait for it.
	need /run/udevd_ready
	echo "Press Enter to start lightdm"; read junk
	echo "* Starting lightdm[$$]"
	exec \
	env - PATH="$PATH" \
	lightdm

Hmm. A tool to wait for a file is needed. So far this should do - /bin/need:

	#!/bin/sh
	i=0
	while ! test -e "$1"; do
		sleep "0.$i"
		test "$i" = 9 || i=$((i+1))
	done

Started it. Confirmed that GUI environment starts and seems to work just fine.

The big one: make system boot without systemd. Final preparations are:
* Create dbus and udevd services, start them only if systemd is not detected.
* Create init scripts. The word "init" here has more than one meaning...

Created /var/service/dbus-daemon service. run file:

	#!/bin/sh
	#exec >/dev/null
	exec 2>&1
	exec </dev/null
	test "`pidof systemd`" && svc -d . && exec sleep 1

	mkdir -p /run/dbus
	echo "* Starting dbus-daemon[$$]"
	exec \
	env - PATH="$PATH" \
	dbus-daemon --nofork --nopidfile --system

I give it the standard log/ even though it does not talk much.
It should auto-shutdown now, since systemd is detected.

Created /var/service/udevd service - its run file:

	#!/bin/sh
	#exec >/dev/null
	exec 2>&1
	exec </dev/null
	test "`pidof systemd`" && svc -d . && exec sleep 1

	mkdir -p /run/udev
	rm -f /run/udev/control # just in case
	rm -f /run/udevd_ready  # just in case
	(
		need /run/udev/control # not sure we really need to wait for it
		echo "Trigger+settle:"
		udevadm --debug trigger --type=subsystems --action=add
		udevadm --debug trigger --type=devices --action=add
		udevadm --debug settle
		>/run/udevd_ready
		echo "Done: trigger+settle"
	) &
	echo "* Starting systemd-udevd[$$]"
	exec \
	env - PATH="$PATH" \
	/usr/lib/systemd/systemd-udevd

It should auto-shutdown now, since systemd is detected.

Created /init script.

	#!/bin/sh
	export PATH=/sbin:/bin:/usr/sbin:/usr/bin

	/etc/runit/1

	exec 0>&- 1>&- 2>&-
	# In this form, shell won't have an open fd to the script file
	exec env - sh -c 'while :; do sleep 9999; done'

Isn't it a cutie.
In the spirit of runit tool, let's run system startup scripts from
/etc/runit/1. Create it:

	#!/bin/sh
	dir_and_not_mounted() {
	        test -d "$1" || return 1
	        ! mountpoint -q -- "$1"
	}
	if fsck -A; then
	        true
	else
	        echo "fsck exit code: $?. Boot will not continue."
	        while true; do sleep 9999; done
	fi
	mount -o remount,rw /
	mount -a
	dir_and_not_mounted /proc && mount -t proc proc /proc
	dir_and_not_mounted /sys && mount -t sysfs sysfs /sys
	# These are mounted by systemd, for some reason not via fstab. Mimic for now:
	dir_and_not_mounted /tmp && mount -t tmpfs tmpfs /tmp
	dir_and_not_mounted /run && mount -t tmpfs tmpfs /run
	# Remove the mess left by systemd which possibly ran in initramfs:
	for d in /sys/fs/cgroup/* /sys/fs/cgroup /sys/kernel/security; do
	        mountpoint -q -- "$d" && umount "$d"
	done
	# initramfs journald shit no one asked for:
	test -d /run/log/journal && rm -rf /run/log/journal
	#
	# Start service supervision
	/var/service/start &

Added "init=/init" to the kernel command line.

Reboot.

Enjoy new view in "ps -AH".


	Reboot/poweroff does not need cooperation with init.

Copied examples/shutdown-1.0 to /app/shutdown-1.0.
Installed /sbin/* symlinks as described in README.


	What's missing or needs improvement?

/var/service/syslog, /var/service/klogd.

"need" (waiting for a file/device/directory/socket to appear) needs to be
a real tool, not a shell loop. Maybe with an optional timeout?
Maybe it already exists?

ifplugd_handler needs a better way to code for the "if service FOO exists,
start it, if it does not, it's fine" idiom.

Admins would need a convenient tool to tail/page service logs just by name.
Something along the lines of

sview:
	#!/bin/sh
	test "$1" || {
	        echo "Syntax: ${0##*/} SERVICE"
	        exit 1
	}
	cd "/var/service/$1" || exit $?
	test -x ./view && exec ./view
	cd "log/logdir" || exit $?
	h=`ttysize h`
	exec tail -n $((h-1)) -F current 2>&1

svpage:
	#!/bin/sh
	test "$1" || {
	        echo "Syntax: ${0##*/} SERVICE"
	        exit 1
	}
	cd "/var/service/$1" || exit $?
	test -x ./page && exec ./page
	test "$PAGER" || PAGER=less
	cd "log/logdir" || exit $?
	cat @* current | $PAGER