On Sat, Sep 17, 2022 at 8:35 PM Yuri Kanivetsky <yuri.kanivetsky@xxxxxxxxx> wrote:
Hi,
I've noticed that an Arch Linux package (gnupg) seemingly
automatically enables a socket:
ln -s "../dirmngr.socket"
"/usr/lib/systemd/user/sockets.target.wants/dirmngr.socket"
https://github.com/archlinux/svntogit-packages/commit/e74444a6851881e2cfea37b76cfb16ba97af2fcc
Before the change they were symlinked to /etc/systemd/user/sockets.target.wants.
Later I was told that there's such a thing as preset units (an
undocumented feature?):
https://bbs.archlinux.org/viewtopic.php?pid=2057758#p2057758
The way I understood it, if I put dirmngr.socket at
/usr/lib/systemd/user/sockets.target.wants, it's like adding "enable
dirmngr.service" to the preset policy. In other words, it won't be
enabled by default, and won't be activated on boot unless I do
`systemctl --user preset dirmngr`.
No, everything linked to a <unit>.wants/ directory immediately becomes a Wants= dep of <unit> and is therefore "enabled", it doesn't matter whether that .wants/ is in /etc or /usr/lib or /run.
In fact, units linked into /usr/.../*.wants/ are enabled permanently, as the sysadmin can no longer `systemctl` disable them at all – they can only be masked. So the Arch change is moving into the opposite direction than what you thought.
Can you clarify this? Are there preset units? Is my understanding of
how they work correct?
It's not entirely correct. Systemd indeed has presets, but they work differently – there are separate config files in /usr/lib/systemd/{user,system}-preset/ that would be read by a `systemctl preset <unit>`. See systemd.preset(5) for details. (For example, https://aur.archlinux.org/cgit/aur.git/tree/?h=softu2f uses presets to enable sockets by default.)
So the reason systemctl says "preset: enabled" is not because of any existing .wants/ symlinks (those still correspond to the main "enabled" status) – instead it's because the unit doesn't match any .preset files that would disable it (i.e. it only matches the compiled-in default "enable *" preset), and therefore systemctl would create a .wants/ symlink from the preset.
Mantas Mikulėnas
