NFS
Server
Using bind mounts
Let's say that we've got one server-machine with 2 directories that we want to share: /mnt/tomoyo and /mnt/kotomi.
First, we have to create a dedicated directory from which our NFS server will access the data:
$ mkdir /export
You may need to change ownership of the /export directory to nobody:nogroup
Then we have to either move our already-existing directories inside /export (using mv from the command line) or bind-mount them there:
{
fileSystems."/export/tomoyo" = {
device = "/mnt/tomoyo";
options = [ "bind" ];
};
fileSystems."/export/kotomi" = {
device = "/mnt/kotomi";
options = [ "bind" ];
};
}
Refer to Filesystems#Bind mounts for more information on bind mounts.
Using btrfs subvolumes
If you are using Btrfs, instead of moving existing directories or bind-mounting them into /export, you can create dedicated subvolumes directly under /export. This avoids the need for additional bind mounts and makes snapshotting or quota management easier. See btrfs#Subvolumes for details on creating subvolumes.
NFS service configuration
Having the filesystem ready, we can proceed to configure the NFS server itself:
{
services.nfs.server.enable = true;
services.nfs.server.exports = ''
/export 192.168.1.10(rw,fsid=0,no_subtree_check) 192.168.1.15(rw,fsid=0,no_subtree_check)
/export/kotomi 192.168.1.10(rw,nohide,insecure,no_subtree_check) 192.168.1.15(rw,nohide,insecure,no_subtree_check)
/export/tomoyo 192.168.1.10(rw,nohide,insecure,no_subtree_check) 192.168.1.15(rw,nohide,insecure,no_subtree_check)
'';
}
This configuration exposes all our shares to 2 local IPs; you can find more examples at Gentoo's wiki on NFS.
To list the current loaded exports, use: exportfs -v
Other options are available on the NixOS option page or via the nixos-option command.
Firewall
If your server-machine has a firewall turned on (as NixOS does by default, for instance), don't forget to open appropriate ports; e.g. for NFSv4:
networking.firewall.allowedTCPPorts = [ 2049 ];
Many clients only support NFSv3, which requires the server to have fixed ports:
services.nfs.server = {
enable = true;
# fixed rpc.statd port; for firewall
lockdPort = 4001;
mountdPort = 4002;
statdPort = 4000;
extraNfsdConfig = '''';
};
networking.firewall = {
enable = true;
# for NFSv3; view with `rpcinfo -p`
allowedTCPPorts = [ 111 2049 4000 4001 4002 20048 ];
allowedUDPPorts = [ 111 2049 4000 4001 4002 20048 ];
};
Client
To ensure the client has the necessary NFS utilities installed, add the following to your system configuration (for example, in configuration.nix).
boot.supportedFilesystems = [ "nfs" ];
NFS shares can be mounted on a client system using the standard filesystem option. Continuing the server example, to mount the tomoyo share:
{
fileSystems."/mnt/tomoyo" = {
device = "server:/tomoyo";
fsType = "nfs";
};
}
In the above configuration, replace "server" with the appropriate IP address or DNS entry of your NFS server. Other, regular filesystem options apply.
Specifying NFS version
You can specify NFS version by adding the "nfsvers=" option:
{
fileSystems."/mnt/tomoyo" = {
# ...
options = [ "nfsvers=4.2" ];
};
}
Lazy-mounting
By default, all shares will be mounted right when your machine starts - apart from being simply unwanted sometimes, this may also cause issues when your computer doesn't have a stable network connection or uses WiFi; you can fix this by telling systemd to mount your shares the first time they are accessed (instead of keeping them mounted at all times):
{
fileSystems."/mnt/tomoyo" = {
# ...
options = [ "x-systemd.automount" "noauto" ];
};
}
Auto-disconnecting
You can tell systemd to disconnect your NFS-client from the NFS-server when the directory has not been accessed for some time:
{
fileSystems."/mnt/tomoyo" = {
# ...
options = [ "x-systemd.idle-timeout=600" ]; # disconnects after 10 minutes (i.e. 600 seconds)
};
}
Using systemd.mounts and systemd.automounts
This section provides an alternative approach for users who prefer to manage mounts using dedicated systemd units. Here is an example with auto-disconnecting and lazy-mounting implemented, and the noatime mount option added.
Note that wantedBy = [ "multi-user.target" ]; is required for the automount unit to start at boot.
Also note that x-systemd mount options are unneeded, as they are a representation of systemd options in fstab(5) format. They get parsed and converted to unit files by systemd-fstab-generator(8) as mentioned in systemd.mount(5).
{
services.rpcbind.enable = true; # needed for NFS
systemd.mounts = [{
type = "nfs";
mountConfig = {
Options = "noatime";
};
what = "server:/tomoyo";
where = "/mnt/tomoyo";
}];
systemd.automounts = [{
wantedBy = [ "multi-user.target" ];
automountConfig = {
TimeoutIdleSec = "600";
};
where = "/mnt/tomoyo";
}];
}
Multiple mounts with the exact same options can benefit from abstraction.
{
services.rpcbind.enable = true; # needed for NFS
systemd.mounts = let commonMountOptions = {
type = "nfs";
mountConfig = {
Options = "noatime";
};
};
in
[
(commonMountOptions // {
what = "server:/tomoyo";
where = "/mnt/tomoyo";
})
(commonMountOptions // {
what = "server:/kotomi";
where = "/mnt/kotomi";
})
];
systemd.automounts = let commonAutoMountOptions = {
wantedBy = [ "multi-user.target" ];
automountConfig = {
TimeoutIdleSec = "600";
};
};
in
[
(commonAutoMountOptions // { where = "/mnt/tomoyo"; })
(commonAutoMountOptions // { where = "/mnt/kotomi"; })
];
}
Nix store on NFS
In a single-user setup (not on Nixos) the Nix store can be also exported over NFS (common in HPC clusters) to share package over the networks. The only requirement is to also pass local_lock=flock or local_lock=all as mount option to allow the nix packages to take locks on modifications. Example entry in fstab:
<host_or_ip>/nix /nix nfs nofail,x-systemd.device-timeout=4,local_lock=all 0 0
TODO: Why this? That seems extremely unsafe. This disables NFS locks (which apply to all NFS clients), and makes locks local, meaning a lock taken by one NFS client isn't seen by another, and both can take their locks. So this removes protection against concurrent writes, which Nix assumes.