pyrox.dev
1# File Systems {#ch-file-systems}
2
3You can define file systems using the `fileSystems` configuration
4option. For instance, the following definition causes NixOS to mount the
5Ext4 file system on device `/dev/disk/by-label/data` onto the mount
6point `/data`:
7
8```nix
9{
10 fileSystems."/data" =
11 { device = "/dev/disk/by-label/data";
12 fsType = "ext4";
13 };
14}
15```
16
17This will create an entry in `/etc/fstab`, which will generate a
18corresponding [systemd.mount](https://www.freedesktop.org/software/systemd/man/systemd.mount.html)
19unit via [systemd-fstab-generator](https://www.freedesktop.org/software/systemd/man/systemd-fstab-generator.html).
20The filesystem will be mounted automatically unless `"noauto"` is
21present in [options](#opt-fileSystems._name_.options). `"noauto"`
22filesystems can be mounted explicitly using `systemctl` e.g.
23`systemctl start data.mount`. Mount points are created automatically if they don't
24already exist. For `device`, it's best to use the topology-independent
25device aliases in `/dev/disk/by-label` and `/dev/disk/by-uuid`, as these
26don't change if the topology changes (e.g. if a disk is moved to another
27IDE controller).
28
29You can usually omit the file system type (`fsType`), since `mount` can
30usually detect the type and load the necessary kernel module
31automatically. However, if the file system is needed at early boot (in
32the initial ramdisk) and is not `ext2`, `ext3` or `ext4`, then it's best
33to specify `fsType` to ensure that the kernel module is available.
34
35::: {.note}
36System startup will fail if any of the filesystems fails to mount,
37dropping you to the emergency shell. You can make a mount asynchronous
38and non-critical by adding `options = [ "nofail" ];`.
39:::
40
41```{=include=} sections
42luks-file-systems.section.md
43sshfs-file-systems.section.md
44overlayfs.section.md
45```