systemd version the issue has been seen with

248.3 (real hardware) and 249.5 (in Virtualbox)

Used distribution

Kubuntu 21.10 and 22.04 (in Virtualbox)

Linux kernel version used

Linux GreenOne 5.13.0-22-generic #22-Ubuntu SMP Fri Nov 5 13:21:36 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Linux kubuntu 5.13.0-19-generic #19-Ubuntu SMP Thu Oct 7 21:58:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

CPU architecture issue was seen on

Intel i9-9880H anbd virtualbox

We create a unit file in home directory and link it to systemd path. It refuses to enable the unit file saying symbolic links are not supported. I am not sure why that is the case but at least the warning is meaningful. Now try to make a unit file in a subdirectory of systemd path (for example /etc/systemd/system/myown.d). It will enable the service file and when you try to run the file, the error is misleading.

I guess the correct behaviour would be catching that systemd is dealing with a linked file already at enabling phase.

Run this as root:

cd ~
cat > test.service <<EOF
[Unit]
Description=Test

[Service]
ExecStart=/bin/sleep infinity

[Install]
WantedBy=multi-user.target
EOF
ln -s test.service /etc/systemd/system/test.service
systemctl daemon-reload
systemctl enable test.service

It gives:

Failed to enable unit: Refusing to operate on alias name or linked unit file: test.service

Now run this:

rm /etc/systemd/system/test.service
cd /etc/systemd/system
mkdir myown.d
cp ~/test.service myown.d/
ln -s myown.d/test.service test.service
systemctl daemon-reload
systemctl enable test.service

it gives:

Created symlink /etc/systemd/system/multi-user.target.wants/test.service → /etc/systemd/system/myown.d/test.service.

Now run

systemctl start test.service

and we get:

Failed to start test.service: Unit test.service not found.