How to auto-mount an NFS share using systemd

If you want to auto-mount an NFS share during boot time, you may run into the issue that by the time the auto-mount procedure is being executed, the network is not yet up and hence the mount of the NFS share will fail. Luckily, there is an easy way around it by using systemd and let it worry about when to mount the share.

The secret lies within some parameters provided alongside the mount directive in /etc/fstab. As you may know, /etc/fstab is used by the Linux kernel to determine what to mount during boot time, and as such, NFS shares can equally be mounted via it. However, if you just provide a regular entry like for a partition or disk, you will run into the issue that the NFS share is being mounted way before the network interfaces have been established.

To overcome that, you want to provide the following parameters inside the /etc/fstab entry:

x-systemd.automount,x-systemd.requires=network-online.target,x-systemd.device-timeout=10s

You can find good documentation of these and more parameters in the Ubuntu manuals. However, in short:

• x-systemd.automount: a systemd automount unit will be created for the file system.
• x-systemd.requires=network-online.target: configures a Requires= and an After= dependency between the created mount unit and the specified other unit. In short, this tells systemd to run the automount after the network is online, meaning that this is the secret sauce to make sure the NFS mount has a network available.
• x-systemd.device-timeout: configures how long systemd should wait for the mount to show up before giving up on the entry from /etc/fstab. You can use units such as ms, s, min, and h, the default is s for seconds.

So, to put it all together, this is the /etc/fstab entry that you are looking for:

<server IP address>:<NFS share> <local mount location> nfs nofail,x-systemd.automount,x-systemd.requires=network-online.target,x-systemd.device-timeout=10s

The nofail is not required anymore for the scenario of the network not being available yet, systemd has taken care of that. However, there can be other reasons for the share not being available, for example, the NFS server itself being unreachable, so nofail is a safe bet to make sure the machine comes up regardless of the NFS mount.

Once you have added the entry in /etc/fstab and rebooted the system, you will find an additional entry reported by the mount command:

systemd-<N> on <local mount location> type autofs (rw,relatime,fd=46,pgrp=1,timeout=0,minproto=5,maxproto=5,direct)