On a live server I have a centos 8.0 installation
which is exported via nfs to a bunch of diskless
clients.
In order to have an independent rw root file system
on each client I have installed the a dracut module
named:
/usr/lib/dracut/modules.d/90overlay-root
which I did manually import from the installation of
the dracut package of a debian buster system.
The provided kernel option 'rootovl' used by the
diskless clients works perfectly.
This is how the mount points look like when a
diskless client mounts the live centos 8 system in
rw mode (client can perform maintenance tasks to
update the live root file system permanently):
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs tmpfs 2.0G 17M 1.9G 1% /run
tmpfs tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
172.16.16.38:/srv/live/cos8 nfs 192G 137G 56G 72% /
tmpfs tmpfs 2.0G 0 2.0G 0% /var/tmp
tmpfs tmpfs 2.0G 0 2.0G 0% /tmp
live:/srv/live/home nfs 192G 137G 56G 72% /home
live:/srv/live/opt nfs 192G 137G 56G 72% /opt
live:/srv/live/root nfs 192G 137G 56G 72% /root
tmpfs tmpfs 392M 0 392M 0% /run/user/0
And this is how the mount points look like when a
diskless client mounts the live centos 8 root file
system in overlay mode using the rootovl kernel option
(client changes to the root fs are not persistent across
reboots):
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 1.9G 0 1.9G 0% /dev
tmpfs tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs tmpfs 2.0G 17M 1.9G 1% /run
tmpfs tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
overlay overlay 2.0G 6.7M 2.0G 1% /
tmpfs tmpfs 2.0G 6.7M 2.0G 1% /live/cow
172.16.16.38:/srv/live/cos8 nfs 192G 137G 56G 72% /live/image
tmpfs tmpfs 2.0G 0 2.0G 0% /tmp
tmpfs tmpfs 2.0G 0 2.0G 0% /var/tmp
live:/srv/live/opt nfs 192G 137G 56G 72% /opt
live:/srv/live/home nfs 192G 137G 56G 72% /home
live:/srv/live/root nfs 192G 137G 56G 72% /root
tmpfs tmpfs 392M 0 392M 0% /run/user/0
As you can see,
/live/image is now the lower ro part of the overlay
(i.e. the live rootnfs mounted in ro mode).
During the shutdown process of a diskless client in
overaly mode I see the following logs almost at the
beginning of it:
[ OK ] Stopped target Remote File System.
Unmounting /live/image... <<<<===!!!
Unmounting /opt...
Unmounting /root...
Unmounting /home...
...
which poses a problem because the ro lower part of
the overlay is unmounted while the overlay (/) is
still active.
In fact,
almost 20% of the time I get a kernel panic error
due to a bunch of missing libraries.
Now,
the question is obvious:
how can I instruct systemd to avoid unmounting
/live/image (or postpone it to a later moment)?
while the diskless client is rebooting or shutting
down?
Thank you.
