File Systems
You can define file systems using the fileSystems
configuration option. For instance, the following definition causes
NixOS to mount the Ext4 file system on device
/dev/disk/by-label/data onto the mount point
/data:
fileSystems."/data" =
{ device = "/dev/disk/by-label/data";
fsType = "ext4";
};
This will create an entry in /etc/fstab, which
will generate a corresponding
systemd.mount
unit via
systemd-fstab-generator.
The filesystem will be mounted automatically unless
"noauto" is present in
options.
"noauto" filesystems can be mounted
explicitly using systemctl e.g.
systemctl start data.mount. Mount points are
created automatically if they don’t already exist. For
device, it’s best to use the topology-independent
device aliases in /dev/disk/by-label and
/dev/disk/by-uuid, as these don’t change if the
topology changes (e.g. if a disk is moved to another IDE
controller).
You can usually omit the file system type
(fsType), since mount can
usually detect the type and load the necessary kernel module
automatically. However, if the file system is needed at early boot
(in the initial ramdisk) and is not ext2,
ext3 or ext4, then it’s best
to specify fsType to ensure that the kernel
module is available.
System startup will fail if any of the filesystems fails to mount,
dropping you to the emergency shell. You can make a mount
asynchronous and non-critical by adding
options = [ "nofail" ];.