[arch-projects] [initscripts] Linux distributions and /run/

Dave Reisner d at falconindy.com
Thu Mar 31 11:08:53 EDT 2011

On Thu, Mar 31, 2011 at 05:04:27PM +0200, Thomas Bächler wrote:
> Am 31.03.2011 16:44, schrieb Tom Gundersen:
> > On systemd systems with initramfs and LVM used, packagers must
> > make sure, that the systemd and initramfs versions match. The initramfs
> > needs to create the /run/ mountpoint for udev to store the data, and
> > mount this tmpfs to /run in the rootfs, so the that the udev database
> > is preserved for the udev version started in the rootfs.
> > ***
> > 
> > The last paragraph is admittedly referring to systemd, but I think
> > this is not important (I think the same case would apply to any init
> > system mounting /run). Here I get the impression that there is
> > something valuable in the udev database that could and should be
> > preserved from initramfs to normal init (I don't fully understand what
> > is happening here, so maybe it does not apply to Arch).
> > 
> >> I was thinking with regard to mdadm now: Maybe mdadm stores some
> >> valuable data there.
> > 
> > They certainly store something in /run, but I don't know what happens
> > if we throw it away at the end of initramfs.
> > 
> >>From all the discussions on this topic I really got the impression
> > that /run is supposed to be created in the initramfs and then
> > preserved until shutdown. Maybe it is worth having a look at what
> > dracut is doing?
> We can do that easily (identical as the /proc, /sys, /dev stuff).
> However, prepare to run into problems when the initramfs udev version
> does not match the version in the system.

Shouldn't be a problem unless there's a format change, as udev can
convert the DB. Relevant snippets from dmesg on my work VM (which i
abuse mercilessly):

udev[36]: starting version 166
<30>udev[462]: converting old udev database
<30>udev[462]: starting version 167


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