[Buildroot] systemd: write-up and packaging questions
André Erdmann
dywi at mailerd.de
Sun Oct 12 17:59:08 UTC 2014
Hi,
Some of the issues pointed out below may be already known, but I couldn't
find any report on this, so I'd like to share my experience with setting up a
systemd-based system that does a little bit more than bringing up a console ;)
Use case was tvheadend with avahi and nfs (+ dropbear etc.), running on a
DreamPlug. Overall it works great, but requires some post-build actions:
* installation of additional service files
(I'll propose patches for them sooner or later)
* changes to the default rootfs skeleton
* optional: removal of /etc/init.d etc.
Filesystem Layout
=================
There are some issues with the default rootfs skeleton.
For example, systemd-hostnamed fails to start with the error message
"file exists", likely related to symlinks pointing to /tmp (/run, /var/...).
After some trial-and-error I've figured out that both /run and /var/tmp
symlinks must be replaced with real directories, and that it needs to be done
before booting systemd (at build/image creation time or in initramfs/initrd).
So, the minimum amount of necessary changes seems to be:
* create /run as directory
and make /var/run->../run, /var/lock->run/lock link to it;
/run gets automatically mounted on boot
* create /var/tmp as directory;
needs manual mount setup (fstab or .mount unit)
* /var/lib/dbus is then a dead link pointing to /tmp/dbus,
not sure if /run/dbus would be the correct link dest
Unit Files
==========
This section is mostly about packaging guidelines,
the manual doesn't answer the questions below.
Installation
------------
systemd's libdir is /lib/system.
Most unit files (.service et al) are installed to /etc/systemd/system,
systemd's own unit files are installed to /lib/systemd/system and some
packages(*) install their files to /usr/lib/systemd/system, which is rather
confusing. Either dir works (search order is /etc > /lib > /usr/lib),
but what's the recommended location?
I'd prefer to have them installed in one dir (systemd's libdir).
(*) grepping yields nginx and connman
Auto-Enabling
-------------
Most packages enable their unit files by default(*), others don't.
Example: lighttpd gets enabled, nginx does not.
Is there any policy for when [not] to enable services?
(*) "ln -s <unit> /etc/systemd/system/<target>.target.wants/<unit>"
Maybe it'd make sense to introduce some SYSTEMD_ variables so that
packages don't have to hardcode/guess systemd file paths, for example:
* SYSTEMD_LIBDIR (= /lib/systemd)
* SYSTEMD_UNITDIR (= $(SYSTEMD_LIBDIR)/system)
* SYSTEMD_CONFDIR (= /etc/systemd)
* SYSTEMD_UNITCONFDIR (= $(SYSTEMD_CONFDIR)/system)
* relpath from <confdir> to <libdir> (= ../..$(SYSTEMD_LIBDIR))
* relpath from <confdir>/system to <libdir>/system (= ../../$(SYSTEMD_UNITDIR))
Bonus: export these variables to post-build scripts
--
André
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