Mounting an NFS Drive at Boot in WSL

The following is the /etc/fstab file I use in a Debian VM to mount a NFS drive from my NAS at boot, which works flawlessly.

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# systemd generates mount units based on this file, see systemd.mount(5).
# Please run 'systemctl daemon-reload' after making changes here.
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
deepdarkfantasy.lan:/volume2/photo /mnt/photos nfs auto,nofail,vers=4.1,noatime,nolock,tcp,actimeo=1800 0 0

However, when I copy this configuration to my Ubuntu WSL, it does not work anymore. To be more precise, the mount -a run by the system during boot fails and returns an error of,

Processing fstab with mount -a failed

which does not provide any information. After WSL boots up, you can manually run sudo mount -a, which works perfectly fine. An easy guess would be that for whatever reason, the network part is not fully initialized when the system is running mount -a. I do not know why this happens or how to fix it on the system level (there might be some relevant issues on GitHub though), but here is the fix.

The fix

To solve this problem, we just have to remove the line from /etc/fstab and run it at startup after network is online.

/etc/wsl.conf approach

/etc/wsl.conf has a [boot] section to host the commands you want to run during startup. We can simply solve the problem by adding the following line to the configuration

[boot]
command = "mount -t nfs -o vers=4.1,noatime,nolock,tcp,actimeo=1800 deepdarkfantasy.lan:/volume2/photo /mnt/photo"

Basically just copy the mount command there. I do not know why this would work, but it just does the job.

A note on systemd

On a normal Linux installation, you can use the network-online.target in systemd to force a service only to run after the network connection is ready. While the current WSL2 already supports systemd (see details here), systemd-networkd-wait-online.service does not really work. It gets stuck in “activating” status, such that services depend on it will not run.