Re: Launch a mount unit from udev rule via ENV{SYSTEMD_WANTS}

[Jacopo <fingolfin00@xxxxxxxxx>]

Il giorno gio 16 feb 2023 alle ore 11:17 Lennart Poettering <lennart@xxxxxxxxxxxxxx> ha scritto:

Matching against "add" is almost certainly wrong, as devices typically
see "change" and other events throughout their early lifetime, and in
that case any settings you make here would get very quickly lost.

In almost all cases you want a check like ACTION!="remove" instead
which matches all "positive" events and ignores the only negative
event.

I updated my udev rule according to your suggestion, but I don't see a different behaviour, still I'll adopt your recommendation in the future.

This is almost certainly an escaping issue.  What's the precisely rule
you are using? It's generally a good idea to start with the line that
doesn't work, not the one that works.

Yes! That was a good point. Removed the minus sign (-) from the mount point (/opt/data-ssd --> /opt/data) and now it works.

Is it a forbidden character in systemd mount points?

Working setup, which means the drive is mounted at boot and if I unplug and then plug in the USB drive at runtime it gets automatically mounted.

- FS label:

   $ e2label /dev/sda1
      data

- udev rule:
  ACTION!="remove", SUBSYSTEM=="block", KERNEL=="sd*", SUBSYSTEMS=="usb", ENV{DEVTYPE}=="partition", IMPORT{builtin}="blkid", ENV{ID_FS_TYPE}=="ext4", ENV{ID_FS_LABEL_ENC}=="data", ENV{SYSTEMD_WANTS}+="opt-data.mount"

- fstab entry:

  LABEL=data  /opt/data  ext4  defaults,nofail,users  0  2

Also working setup.

- FS label:

   $ e2label /dev/sda1
      data-ssd

- udev rule:

  ACTION!="remove", SUBSYSTEM=="block", KERNEL=="sd*", SUBSYSTEMS=="usb", ENV{DEVTYPE}=="partition", IMPORT{builtin}="blkid", ENV{ID_FS_TYPE}=="ext4", ENV{ID_FS_LABEL_ENC}=="data-ssd", ENV{SYSTEMD_WANTS}+="opt-data.mount

- fstab entry:

  LABEL=data-ssd  /opt/data  ext4  defaults,nofail,users  0  2

But not working.

- FS label:

  $ e2label /dev/sda1
     data

- udev rule:

  ACTION!="remove", SUBSYSTEM=="block", KERNEL=="sd*", SUBSYSTEMS=="usb", ENV{DEVTYPE}=="partition", IMPORT{builtin}="blkid", ENV{ID_FS_TYPE}=="ext4", ENV{ID_FS_LABEL_ENC}=="data", ENV{SYSTEMD_WANTS}+="opt-data\x2dssd.mount"

- fstab entry:

  LABEL=data /opt/data-ssd  ext4  defaults,nofail,users  0  2

For the not working case udev rule I tested both ENV{SYSTEMD_WANTS}+="opt-data-ssd.mount" and ENV{SYSTEMD_WANTS}+="opt-data\x2dssd.mount", but no difference.

And I can print the generated mount unit only with the unicode minus sign "\x2d" in the unit name:

$ sudo systemctl cat "opt-data\x2dssd.mount"
  # /run/systemd/generator/opt-data\x2dssd.mount
  # Automatically generated by systemd-fstab-generator

  [Unit]
  Documentation=man:fstab(5) man:systemd-fstab-generator(8)
  SourcePath=/etc/fstab
  Requires=systemd-fsck@dev-disk-by\x2dlabel-data.service
  After=systemd-fsck@dev-disk-by\x2dlabel-data.service
  After=blockdev@dev-disk-by\x2dlabel-data.target

  [Mount]
  What=/dev/disk/by-label/data
  Where=/opt/data-ssd
  Type=ext4
  Options=defaults,nofail,users

While

$ sudo systemctl cat "opt-data-ssd.mount"
   No files found for opt-data-ssd.mount.

 

Also, 244 is ancient 4y old stuff. Consider updating.

Yes true, unfortunately I'm confined to systemd 244 in my application for the time being, but I replicated the same configuration on my laptop running systemd 252 (same SATA disk and adapter) and the behavior is identical.

Thanks for your insight.