[systemd-devel] systemd is trying to break mount ordering

[Lennart Poettering]

On Mon, 15.06.15 13:24, Jan Synáček (jsynacek at redhat.com) wrote:

> 
> I have the following setup on a freshly updated Fedora Rawhide machine
> with systemd-220-9.fc23.x86_64.
> 
> # cat /etc/fstab
> [comments left out]
> UUID=d5ac823b-d0bd-4f7f-bf4b-5cc82d585a92 /                       btrfs   subvol=root     0 0
> UUID=ec79f233-055c-40fa-98e5-e2d77314913a /boot                   ext4    defaults        1 2
> UUID=d5ac823b-d0bd-4f7f-bf4b-5cc82d585a92 /home                   btrfs   subvol=home     0 0
> 192.168.122.1:/srv/nfs /mnt/nfs nfs defaults 0 0
> /var/tmp/test.iso /mnt/nfs/content iso9660 loop,ro 0 0
> 
> Notice the last two lines. There is an NFS mount mounted to /mnt/nfs and
> an ISO filesystem mounted into /mnt/nfs/content, which makes it
> dependent on the NFS mount.

Please add "_netdev" to the mount options of the ISO mount, to let
systemd know that you need the network for that.

Otherwise systemd assumes the ISO mount is in fact a local mount
(which is hence ordered before local-fs.target which in turn is before
basic.target), while correctly detecting that the nfs mount is a
remote mount (which is henece ordered before remote-fs.target which in
turn is usually assumed to be started much later than
local-fs.target). Since however the local mount is ordered after the
remote mounts you get a cyclic dep loop.

> Isn't systemd trying to delete too many jobs while resolving the cycles?

Well, systemd removes jobs effectively randomly, since for the cycle
breaking logic all units are the same. Of course, you might consider
some jobs more important than others, but systemd doesn't know which
ones those would be.

There have been prior requests for a better cycle breaking strategy
but so far I am not aware of any proposal that could really work and
substantially better things.

Lennart

-- 
Lennart Poettering, Red Hat