Got some more time to poke around the system. If did change the
ExecStart in /lib/systemd/system/systemd-udevd.service to:
ExecStart=/lib/systemd/systemd-udevd --debug
`journalctl -u systemd-udevd` now contains this:
Apr 01 13:56:58 alice systemd-udevd[424]: worker [458]
** Attachment added: usb.out
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1433557/+attachment/4362912/+files/usb.out
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https://bugs.launchpad.net/bugs/1433557
Title:
** Attachment added: systemd-udevd.log
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1433557/+attachment/4362913/+files/systemd-udevd.log
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trace attached.
However, the trace shows that it existed almost instantly and normally.
So I disabled the udev rule again and reboot. This time around it did
again end up with the boot wait. So it seems that the accel udev rule is
only a coincident.
** Attachment added: accel.trace
Ah-haa! For the first two workers I found these gems in the log:
Apr 01 13:58:57 alice systemd-udevd[458]: timeout '/bin/sh -c 'if [ -f
/usr/bin/systemctl ]; then /usr/bin/systemctl --no-block start
hplip-printer@003:006.service; else /usr/bin/nohup
/usr/bin/hp-config_usb_printer 003:006 ; fi
