nixos/doc: add section on sshfs file systems
This documents how to use sshfs a bit and how to set up an automatically mounted sshfs filesystem in NixOS. Also it closes #125905.
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rnhmjoj
Ryan Mulligan
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@ -54,4 +54,5 @@
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</para>
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</note>
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<xi:include href="luks-file-systems.xml" />
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<xi:include href="../from_md/configuration/sshfs-file-systems.section.xml" />
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</chapter>
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104
nixos/doc/manual/configuration/sshfs-file-systems.section.md
Normal file
104
nixos/doc/manual/configuration/sshfs-file-systems.section.md
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@ -0,0 +1,104 @@
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# SSHFS File Systems {#sec-sshfs-file-systems}
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[SSHFS][sshfs] is a [FUSE][fuse] filesystem that allows easy access to directories on a remote machine using the SSH File Transfer Protocol (SFTP).
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It means that if you have SSH access to a machine, no additional setup is needed to mount a directory.
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[sshfs]: https://github.com/libfuse/sshfs
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[fuse]: https://en.wikipedia.org/wiki/Filesystem_in_Userspace
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## Interactive mounting {#sec-sshfs-interactive}
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In NixOS, SSHFS is packaged as <package>sshfs</package>.
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Once installed, mounting a directory interactively is simple as running:
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```ShellSession
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$ sshfs my-user@example.com:/my-dir /mnt/my-dir
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```
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Like any other FUSE file system, the directory is unmounted using:
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```ShellSession
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$ fusermount -u /mnt/my-dir
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```
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## Non-interactive mounting {#sec-sshfs-non-interactive}
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Mounting non-interactively requires some precautions because `sshfs` will run at boot and under a different user (root).
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For obvious reason, you can't input a password, so public key authentication using an unencrypted key is needed.
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To create a new key without a passphrase you can do:
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```ShellSession
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$ ssh-keygen -t ed25519 -P '' -f example-key
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Generating public/private ed25519 key pair.
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Your identification has been saved in test-key
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Your public key has been saved in test-key.pub
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The key fingerprint is:
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SHA256:yjxl3UbTn31fLWeyLYTAKYJPRmzknjQZoyG8gSNEoIE my-user@workstation
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```
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To keep the key safe, change the ownership to `root:root` and make sure the permissions are `600`:
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OpenSSH normally refuses to use the key if it's not well-protected.
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The file system can be configured in NixOS via the usual [fileSystems](options.html#opt-fileSystems) option.
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Here's a typical setup:
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```nix
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{
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system.fsPackages = [ pkgs.sshfs ];
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fileSystems."/mnt/my-dir" = {
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device = "my-user@example.com:/my-dir/";
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fsType = "sshfs";
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options =
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[ # Filesystem options
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"allow_other" # for non-root access
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"_netdev" # this is a network fs
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"x-systemd.automount" # mount on demand
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# SSH options
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"reconnect" # handle connection drops
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"ServerAliveInterval=15" # keep connections alive
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"IdentityFile=/var/secrets/example-key"
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];
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};
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}
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```
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More options from `ssh_config(5)` can be given as well, for example you can change the default SSH port or specify a jump proxy:
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```nix
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{
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options =
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[ "ProxyJump=bastion@example.com"
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"Port=22"
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];
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}
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```
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It's also possible to change the `ssh` command used by SSHFS to connect to the server.
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For example:
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```nix
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{
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options =
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[ (builtins.replaceStrings [" "] ["\\040"]
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"ssh_command=${pkgs.openssh}/bin/ssh -v -L 8080:localhost:80")
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];
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}
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```
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::: {.note}
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The escaping of spaces is needed because every option is written to the `/etc/fstab` file, which is a space-separated table.
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:::
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### Troubleshooting {#sec-sshfs-troubleshooting}
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If you're having a hard time figuring out why mounting is failing, you can add the option `"debug"`.
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This enables a verbose log in SSHFS that you can access via:
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```ShellSession
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$ journalctl -u $(systemd-escape -p /mnt/my-dir/).mount
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Jun 22 11:41:18 workstation mount[87790]: SSHFS version 3.7.1
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Jun 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>
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Jun 22 11:41:19 workstation mount[87793]: my-user@example.com: Permission denied (publickey).
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Jun 22 11:41:19 workstation mount[87790]: read: Connection reset by peer
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Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Mount process exited, code=exited, status=1/FAILURE
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Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Failed with result 'exit-code'.
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Jun 22 11:41:19 workstation systemd[1]: Failed to mount /mnt/my-dir.
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Jun 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.
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```
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::: {.note}
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If the mount point contains special characters it needs to be escaped using `systemd-escape`.
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This is due to the way systemd converts paths into unit names.
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:::
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@ -0,0 +1,139 @@
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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-sshfs-file-systems">
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<title>SSHFS File Systems</title>
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<para>
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<link xlink:href="https://github.com/libfuse/sshfs">SSHFS</link> is
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a
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<link xlink:href="https://en.wikipedia.org/wiki/Filesystem_in_Userspace">FUSE</link>
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filesystem that allows easy access to directories on a remote
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machine using the SSH File Transfer Protocol (SFTP). It means that
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if you have SSH access to a machine, no additional setup is needed
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to mount a directory.
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</para>
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<section xml:id="sec-sshfs-interactive">
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<title>Interactive mounting</title>
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<para>
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In NixOS, SSHFS is packaged as <package>sshfs</package>. Once
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installed, mounting a directory interactively is simple as
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running:
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</para>
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<programlisting>
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$ sshfs my-user@example.com:/my-dir /mnt/my-dir
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</programlisting>
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<para>
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Like any other FUSE file system, the directory is unmounted using:
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</para>
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<programlisting>
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$ fusermount -u /mnt/my-dir
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</programlisting>
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</section>
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<section xml:id="sec-sshfs-non-interactive">
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<title>Non-interactive mounting</title>
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<para>
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Mounting non-interactively requires some precautions because
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<literal>sshfs</literal> will run at boot and under a different
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user (root). For obvious reason, you can’t input a password, so
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public key authentication using an unencrypted key is needed. To
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create a new key without a passphrase you can do:
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</para>
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<programlisting>
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$ ssh-keygen -t ed25519 -P '' -f example-key
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Generating public/private ed25519 key pair.
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Your identification has been saved in test-key
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Your public key has been saved in test-key.pub
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The key fingerprint is:
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SHA256:yjxl3UbTn31fLWeyLYTAKYJPRmzknjQZoyG8gSNEoIE my-user@workstation
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</programlisting>
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<para>
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To keep the key safe, change the ownership to
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<literal>root:root</literal> and make sure the permissions are
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<literal>600</literal>: OpenSSH normally refuses to use the key if
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it’s not well-protected.
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</para>
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<para>
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The file system can be configured in NixOS via the usual
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<link xlink:href="options.html#opt-fileSystems">fileSystems</link>
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option. Here’s a typical setup:
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</para>
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<programlisting language="bash">
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{
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system.fsPackages = [ pkgs.sshfs ];
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fileSystems."/mnt/my-dir" = {
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device = "my-user@example.com:/my-dir/";
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fsType = "sshfs";
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options =
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[ # Filesystem options
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"allow_other" # for non-root access
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"_netdev" # this is a network fs
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"x-systemd.automount" # mount on demand
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# SSH options
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"reconnect" # handle connection drops
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"ServerAliveInterval=15" # keep connections alive
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"IdentityFile=/var/secrets/example-key"
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];
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};
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}
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</programlisting>
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<para>
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More options from <literal>ssh_config(5)</literal> can be given as
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well, for example you can change the default SSH port or specify a
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jump proxy:
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</para>
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<programlisting language="bash">
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{
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options =
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[ "ProxyJump=bastion@example.com"
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"Port=22"
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];
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}
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</programlisting>
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<para>
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It’s also possible to change the <literal>ssh</literal> command
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used by SSHFS to connect to the server. For example:
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</para>
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<programlisting language="bash">
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{
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options =
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[ (builtins.replaceStrings [" "] ["\\040"]
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"ssh_command=${pkgs.openssh}/bin/ssh -v -L 8080:localhost:80")
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];
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}
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</programlisting>
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<note>
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<para>
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The escaping of spaces is needed because every option is written
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to the <literal>/etc/fstab</literal> file, which is a
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space-separated table.
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</para>
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</note>
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<section xml:id="sec-sshfs-troubleshooting">
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<title>Troubleshooting</title>
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<para>
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If you’re having a hard time figuring out why mounting is
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failing, you can add the option
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<literal>"debug"</literal>. This enables a verbose log
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in SSHFS that you can access via:
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</para>
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<programlisting>
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$ journalctl -u $(systemd-escape -p /mnt/my-dir/).mount
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Jun 22 11:41:18 workstation mount[87790]: SSHFS version 3.7.1
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Jun 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>
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Jun 22 11:41:19 workstation mount[87793]: my-user@example.com: Permission denied (publickey).
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Jun 22 11:41:19 workstation mount[87790]: read: Connection reset by peer
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Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Mount process exited, code=exited, status=1/FAILURE
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Jun 22 11:41:19 workstation systemd[1]: mnt-my\x2ddir.mount: Failed with result 'exit-code'.
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Jun 22 11:41:19 workstation systemd[1]: Failed to mount /mnt/my-dir.
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Jun 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.
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</programlisting>
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<note>
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<para>
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If the mount point contains special characters it needs to be
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escaped using <literal>systemd-escape</literal>. This is due
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to the way systemd converts paths into unit names.
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</para>
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</note>
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</section>
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</section>
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</section>
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