DOKK / manpages / debian 12 / nbdkit / nbdkit-ssh-plugin.1.en
nbdkit-ssh-plugin(1) NBDKIT nbdkit-ssh-plugin(1)

nbdkit-ssh-plugin - access disk images over the SSH protocol

 nbdkit ssh host=HOST [path=]PATH
            [compression=true] [config=CONFIG_FILE]
            [create=true] [create-mode=MODE] [create-size=SIZE]
            [identity=FILENAME] [known-hosts=FILENAME]
            [password=PASSWORD|-|+FILENAME]
            [port=PORT] [timeout=SECS] [user=USER]
            [verify-remote-host=false]

This is an nbdkit(1) plugin which lets you access remote disk images over Secure Shell (SSH). Any server which hosts disk images and runs an SSH server can be turned into an NBD source using this plugin.

Open a file called disk.img on remote host "ssh.example.com". Because the pathname is relative, it is opened relative to the user’s home directory on the remote server.

The remote file can be read or written. To force read-only access add the -r flag.

As above but log in using username "bob" (instead of trying the local username).

Enable compression. You should only use this on slow or bandwidth-limited connections. On fast connections it will slow things down.
Read local SSH configuration from an alternate configuration file. Libssh expands some "%"-sequences in "CONFIG_FILE", see "Path expansion" below. "CONFIG_FILE" must expand to an absolute path.
Do not read any local SSH configuration.

The "config" parameter is optional. If it is not specified at all then ~/.ssh/config and /etc/ssh/ssh_config are both read. Missing or unreadable files are ignored.

(nbdkit ≥ 1.32)

If set, the remote file will be created. The remote file is created on the first NBD connection to nbdkit, not when nbdkit starts up. If the file already exists, it will be replaced and any existing content lost.

If using this option, you must use "create-size". "create-mode" can be used to control the permissions of the new file.

(nbdkit ≥ 1.32)

If using "create=true" specify the default permissions of the new remote file. You can use octal modes like "create-mode=0777" or "create-mode=0644". The default is 0600, ie. only readable and writable by the remote user.

(nbdkit ≥ 1.32)

If using "create=true", specify the virtual size of the new disk. "SIZE" can use modifiers like "100M" etc.

Specify the name or IP address of the remote host.

This parameter is required.

Prepend the private key (identity) "FILENAME" to the list of identity files used. Libssh examines several identity files by default such as ~/.ssh/id_ed25519, ~/.ssh/id_ecdsa, ~/.ssh/id_rsa and ~/.ssh/id_dsa. Libssh expands some "%"-sequences in "FILENAME", see "Path expansion" below. "FILENAME" must expand to an absolute path.

You can give this parameter multiple times.

Set name of the file which records the identity of previously seen hosts. Libssh expands some "%"-sequences in "FILENAME", see "Path expansion" below. "FILENAME" must expand to an absolute path.

The default is to check ~/.ssh/known_hosts followed by /etc/ssh/ssh_known_hosts.

Set the password to use when connecting to the remote server.

Note that passing this on the command line is not secure on shared machines.

Ask for the password (interactively) when nbdkit starts up.
Read the password from the named file. This is a secure method to supply a password, as long as you set the permissions on the file appropriately.
Read the password from file descriptor number "FD", inherited from the parent process when nbdkit starts up. This is also a secure method to supply a password.
[path=]PATH
Specify the path to the remote file. This can be a relative path in which case it is relative to the remote home directory.

This parameter is required.

"path=" is a magic config key and may be omitted in most cases. See "Magic parameters" in nbdkit(1).

Specify the SSH protocol port name or number.

This parameter is optional. If not given then the default ssh port is used.

Set the SSH connection timeout in seconds.
Specify the remote username.

This parameter is optional. If not given then the local username is used.

Set whether or not we verify the remote host is one we have previously seen, using a local file such as ~/.ssh/known_hosts. The default is "true", meaning that we verify the remote host’s identity has not changed.

Setting this to "false" is dangerous because it allows a Man-In-The-Middle (MITM) attack to be conducted against you.

The SSH server’s host key is checked at connection time, and must be present and correct in the local "known hosts" file.

If you have never connected to the SSH server before then the connection will usually fail. You can:

  • connect to the server first using ssh(1) so you can manually accept the host key, or
  • provide the host key in an alternate file which you specify using the "known-hosts" option, or
  • set verify-remote-host=false on the command line. This latter option is dangerous because it allows a MITM attack to be conducted against you.

This plugin supports only the following authentication methods: "none", "publickey" or "password". In particular note that "keyboard-interactive" is not supported.

SSH agent

There is no means for nbdkit to ask for the public key passphrase when it is running as a server. Therefore "publickey" authentication must be done in conjunction with ssh-agent(1).

In the "config", "identity" and "known-hosts" options, libssh expands some "%"-sequences.

%d
The user’s SSH directory, usually ~/.ssh
%u
The local username.
%l
The local hostname.
%h
The remote hostname.
%r
The remote username.
%p
The SSH port number.
"%%"
In libssh > 0.9.0 this expands to a single "%" character. In earlier versions of libssh there was no way to escape a "%" character.

-D ssh.log=[1..4]

Set the libssh log level to increasing levels of verbosity. Each level includes messages from the previous levels. Currently the levels are:

1
informational and warning messages
2
SSH and SFTP protocol steps
3
SSH and SFTP packets
4
libssh functions

Use level 2 to diagnose SSH protocol or server problems. Levels 3 and 4 are extremely verbose and probably only useful if you are debugging libssh itself.

If diagnosing SSH problems it is also useful to look at server-side logs, eg. /var/log/secure or "journalctl -u sshd"

~/.ssh/config
/etc/ssh/ssh_config
These are the default SSH config files which are read to get other options. You can change this using the "config" option.
~/.ssh/id_dsa
~/.ssh/id_ecdsa
~/.ssh/id_ed25519
~/.ssh/id_rsa
These are some of the default private key (identify) files used by libssh. You can prepend more to the list using the "identity" option.
~/.ssh/known_hosts
/etc/ssh/ssh_known_hosts
These are the default SSH files recording the identity of previously seen hosts. You can change this using the "known-hosts" option.
$plugindir/nbdkit-ssh-plugin.so
The plugin.

Use "nbdkit --dump-config" to find the location of $plugindir.

"nbdkit-ssh-plugin" first appeared in nbdkit 1.12.

nbdkit(1), nbdkit-curl-plugin(1), nbdkit-extentlist-filter(1), nbdkit-retry-filter(1), nbdkit-plugin(3), ssh(1), ssh-agent(1), https://libssh.org.

Richard W.M. Jones

Parts derived from Pino Toscano’s qemu libssh driver.

Copyright (C) 2014-2020 Red Hat Inc.

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2023-01-04 nbdkit-1.32.5