[systemd-devel] Using btrfs subvolumes with systemd

[Florent Peterschmitt]

8 juin 2016 20:57 "Florent Peterschmitt" <florent at peterschmitt.fr> a écrit:
> Hi,
> 
> I have a recurrent problem at boot time, when mounting filesystems.
> 
> First :
> 
> o This problem was on systemd v229 and is still here with v230
> o I use BTRFS for everything
> o I have 6 subvolumes
> o I use a subvolume as root filesystem, then mount other subvolumes
> o I use Gentoo as main distribution.
> 
> Here are some outputs:
> 
> # btrfs subvolume list /
> ID 257 gen 90 top level 5 path archlinux
> ID 258 gen 4296 top level 5 path gentoo
> ID 259 gen 2715 top level 5 path lib.modules
> ID 260 gen 4225 top level 5 path SteamLibrary
> ID 261 gen 613 top level 5 path ubuntu
> ID 262 gen 2875 top level 5 path usr.src
> 
> # cat /etc/fstab 
> /dev/mapper/root / btrfs autodefrag,noatime,subvol=gentoo 0 0
> tmpfs /var/tmp/portage/ tmpfs defaults 0 0
> UUID=98c23f22-566e-4a17-b663-3c0ce781a897 /boot ext4 defaults,noatime,nodev 0 0
> /dev/mapper/root /lib64/modules btrfs autodefrag,noatime,subvol=lib.modules 0 0
> /dev/mapper/root /usr/src btrfs autodefrag,noatime,subvol=usr.src 0 0
> /dev/mapper/root /home/florent/SteamLibrary btrfs autodefrag,noatime,subvol=SteamLibrary 0 0
> 
> /dev/cdrom /mnt/cdrom auto noauto,ro 0 0
> /dev/fd0 /mnt/floppy auto noauto 0 0
> 
> As you can see, /dev/mapper/root is the btrfs filesystem, created with "mkfs.btrfs
> /dev/mapper/root", nothing special. Same for subvolumes.
> 
> Here is the problem:
> 
> Each time i boot, this error happen:
> # journalctl -xe
> [...]
> systemd[1]: dev-mapper-root.device: Job dev-mapper-root.device/start timed out.
> systemd[1]: Timed out waiting for device /dev/mapper/root.
> [...]
> 
> After StartExecTimeout (reduced to 10s…), i'm dropped into an emergency shell. There, i fire "mount
> -a", then quit, and the system boots.
> 
> But only gentoo does continue booting, with ArchLinux (v230 too), i'm simply dropped into emergency
> shell forever until i mask usr-src.mount and lib-modules.mount before quitting!
> 
> Is this a miss-configuration or a problem with systemd's device handling?
> 
> Thanks.
> 
> Florent Peterschmitt

I forgot to mention that i use this workaround:

ln -s /dev/mapper/root /etc/dev-usr-src
ln -s /dev/mapper/root /etc/dev-lib-modules
ln -s /dev/mapper/root /etc/dev-steam

Then adapt /etc/fstab to use /etc/dev-* instead of /dev/mapper/root

Florent Peterschmitt