[systemd-devel] udev device mapper rules for early boot?

[Colin Guthrie]

'Twas brillig, and Nikolaus Rath at 11/12/12 16:31 did gyre and gimble:
> On 12/11/2012 03:00 AM, Colin Guthrie wrote:
>> 'Twas brillig, and Nikolaus Rath at 10/12/12 19:03 did gyre and gimble:
>>> Hello,
>>>
>>> I have created a udev rule to set the owner of a specific block device:
>>>
>>> SUBSYSTEM=="block",
>>> ENV{DM_UUID}=="LVM-yYuoI8k05GWxZnz9BeEIwPUGGeojzF3dZZmXTYRqC051Tllj76OHdDlzYhKZUu7u",
>>> OWNER="1000"
>>>
>>> If I disable and re-enable this logical volume with lvchange, it gets
>>> created with the correct owner.
>>>
>>> However, when I boot the computer, the device is always owned by
>>> root:disk instead.
>>>
>>> I checked my initrd, and the rule is present in lib/udev/rules.d as
>>> 99-udev-custom.rules.
>>>
>>> Does anyone have a suggestion of how I could debug this further? Why is
>>> my rule ignored when the volume comes up the first time?
>> Random guess: does that user exist in the context of the initrd?

> No. But that shouldn't be a problem. The other rules in the initrd also
> refer to non-existing users (e.g. disk).

Are you sure that "disk" is the user here and not the group? Keep in
mind that dracut copies /etc/group to the initrd but only includes a cut
down /etc/passwd with just root and nobody defined...

> I guess udev just waits until
> passwd becomes available. Also, I tried specifying the UID instead of
> the name, but that didn't help either.

I don't think udev "waits until passwd becomes available". It's just a
hit and hope effort AFAIUI.

You'll need to teach your initrd about your user if you want it to be
owned by your user (i.e. somehow modify the dracut module
modules.d/99base/module-setup.sh or better add a new module "99myuser"
or whatever, that is just a basic stub that just adds your user - that
way your change survives distro updates).

If you don't really care about the owner and the group is actually
enough for your needs then that should work fine (due to dracut copying
/etc/group from your system) - assuming of course that's where your
group is defined and it's not on some LDAP or YP/NIS system somewhere.

Col

-- 

Colin Guthrie
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http://colin.guthr.ie/

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