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1# SSHFS File Systems {#sec-sshfs-file-systems}
2
3[SSHFS][sshfs] is a [FUSE][fuse] filesystem that allows easy access to directories on a remote machine using the SSH File Transfer Protocol (SFTP).
4It means that if you have SSH access to a machine, no additional setup is needed to mount a directory.
5
6[sshfs]: https://github.com/libfuse/sshfs
7[fuse]: https://en.wikipedia.org/wiki/Filesystem_in_Userspace
8
9## Interactive mounting {#sec-sshfs-interactive}
10
11In NixOS, SSHFS is packaged as `sshfs`.
12Once installed, mounting a directory interactively is simple as running:
13```ShellSession
14$ sshfs my-user@example.com:/my-dir /mnt/my-dir
15```
16Like any other FUSE file system, the directory is unmounted using:
17```ShellSession
18$ fusermount -u /mnt/my-dir
19```
20
21## Non-interactive mounting {#sec-sshfs-non-interactive}
22
23Mounting non-interactively requires some precautions because `sshfs` will run at boot and under a different user (root).
24For obvious reason, you can't input a password, so public key authentication using an unencrypted key is needed.
25To create a new key without a passphrase you can do:
26```ShellSession
27$ ssh-keygen -t ed25519 -P '' -f example-key
28Generating public/private ed25519 key pair.
29Your identification has been saved in example-key
30Your public key has been saved in example-key.pub
31The key fingerprint is:
32SHA256:yjxl3UbTn31fLWeyLYTAKYJPRmzknjQZoyG8gSNEoIE my-user@workstation
33```
34To keep the key safe, change the ownership to `root:root` and make sure the permissions are `600`:
35OpenSSH normally refuses to use the key if it's not well-protected.
36
37The file system can be configured in NixOS via the usual [fileSystems](#opt-fileSystems) option.
38Here's a typical setup:
39```nix
40{
41 fileSystems."/mnt/my-dir" = {
42 device = "my-user@example.com:/my-dir/";
43 fsType = "sshfs";
44 options =
45 [ # Filesystem options
46 "allow_other" # for non-root access
47 "_netdev" # this is a network fs
48 "x-systemd.automount" # mount on demand
49
50 # SSH options
51 "reconnect" # handle connection drops
52 "ServerAliveInterval=15" # keep connections alive
53 "IdentityFile=/var/secrets/example-key"
54 ];
55 };
56}
57```
58More options from `ssh_config(5)` can be given as well, for example you can change the default SSH port or specify a jump proxy:
59```nix
60{
61 options =
62 [ "ProxyJump=bastion@example.com"
63 "Port=22"
64 ];
65}
66```
67It's also possible to change the `ssh` command used by SSHFS to connect to the server.
68For example:
69```nix
70{
71 options =
72 [ (builtins.replaceStrings [" "] ["\\040"]
73 "ssh_command=${pkgs.openssh}/bin/ssh -v -L 8080:localhost:80")
74 ];
75
76}
77```
78
79::: {.note}
80The escaping of spaces is needed because every option is written to the `/etc/fstab` file, which is a space-separated table.
81:::
82
83### Troubleshooting {#sec-sshfs-troubleshooting}
84
85If you're having a hard time figuring out why mounting is failing, you can add the option `"debug"`.
86This enables a verbose log in SSHFS that you can access via:
87```ShellSession
88$ journalctl -u $(systemd-escape -p /mnt/my-dir/).mount
89Jun 22 11:41:18 workstation mount[87790]: SSHFS version 3.7.1
90Jun 22 11:41:18 workstation mount[87793]: executing <ssh> <-x> <-a> <-oClearAllForwardings=yes> <-oServerAliveInterval=15> <-oIdentityFile=/var/secrets/wrong-key> <-2> <my-user@example.com> <-s> <sftp>
91Jun 22 11:41:19 workstation mount[87793]: my-user@example.com: Permission denied (publickey).
92Jun 22 11:41:19 workstation mount[87790]: read: Connection reset by peer
93Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Mount process exited, code=exited, status=1/FAILURE
94Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Failed with result 'exit-code'.
95Jun 22 11:41:19 workstation systemd[1]: Failed to mount /mnt/my-dir.
96Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Consumed 54ms CPU time, received 2.3K IP traffic, sent 2.7K IP traffic.
97```
98
99::: {.note}
100If the mount point contains special characters it needs to be escaped using `systemd-escape`.
101This is due to the way systemd converts paths into unit names.
102:::