[systemd-devel] Unable to override systemd-udevd.service

[Kirill Elagin]

While playing with this I've also noticed that systemd treats symlinks in a
bit
weird way: looks like if it sees a symlink it dereferences it, but not all
the symlinks
in the path. Here is an example:

# systemctl show systemd-udevd.service -p FragmentPath
FragmentPath=/usr/lib64/systemd/system/systemd-udevd.service
# ln -s /usr/lib/systemd/system/systemd-udevd.service /etc/systemd/system
# systemctl daemon-reload
# systemctl show systemd-udevd.service -p FragmentPath
FragmentPath=/usr/lib/systemd/system/systemd-udevd.service
# readlink -f /etc/systemd/system/systemd-udevd.service
/usr/lib64/systemd/system/systemd-udevd.service

I feel that I'm interested in the _reason_ why this unit is loaded, that
is, I guess,
I'd like to see `/etc/systemd/system/system-udevd.service` in this case, as
it
_explains why_ systemd loaded this unit.
But what I see is `/usr/lib/systemd/system/systemd-udevd.service` which is
totally unhelpful as it is neither the path that systemd used to discover
the unit,
nor the actual path to the unit file (which is `/usr/lib64/…`).
(Here, on Gentoo, `/usr/lib` is a symlink to `/usr/lib64`.)

Probably, somehow using this and the fact that if `cp`'s target is a
symlink,
then the symlink's target will be overwritten with the symlink left where
it was,
it is possible to reproduce the issue.


--
Кирилл Елагин


On Wed, Apr 23, 2014 at 8:43 AM, Lennart Poettering
<lennart at poettering.net>wrote:

> On Sun, 30.03.14 19:23, Andrey Borzenkov (arvidjaar at gmail.com) wrote:
>
> > linux-qbc6:~ # systemctl show systemd-udevd.service -p FragmentPath
> > FragmentPath=/usr/lib/systemd/system/systemd-udevd.service
> > linux-qbc6:~ # cp /usr/lib/systemd/system/systemd-udevd.service
> /etc/systemd/system
> > linux-qbc6:~ # systemctl daemon-reload
> > linux-qbc6:~ # cp /usr/lib/systemd/system/systemd-udevd.service
> /etc/systemd/system
> > linux-qbc6:~ # systemctl show systemd-udevd.service -p FragmentPath
> > FragmentPath=/usr/lib/systemd/system/systemd-udevd.service
> > linux-qbc6:~ # exit
> >
> > >From non-exhaustive testing it appears to be the only unit showing this
> > property. Enabling systemd debug does not add any useful information
> > (no output about unit discovery). Any way to debug it?
> >
> > The version is systemd-208-19.1.x86_64 from openSUSE.
>
> Hmm, that's weird. Is /etc on some weird mount point or so?
>
> It might be interesting to run "strace -o log -e open -p 1" and then
> trigger a
> reload, and then look at the generate log file "log". It should show you
> where systemd is looking for the udev service file, and might contain a
> hint, why it skips the file in /etc?
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
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