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nbdkit-ssh-plugin(1) NBDKIT nbdkit-ssh-plugin(1)

NAME

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

SYNOPSIS

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

DESCRIPTION

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.

EXAMPLES

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).

PARAMETERS

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.

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.

NOTES

Known hosts

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.

Supported authentication methods

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).

Path expansion

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.

DEBUG FLAGS

-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"

FILES

~/.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.

VERSION

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

SEE ALSO

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

AUTHORS

Richard W.M. Jones

Parts derived from Pino Toscano’s qemu libssh driver.

COPYRIGHT

Copyright (C) 2014-2020 Red Hat Inc.

LICENSE

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
  • Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

2022-04-16 nbdkit-1.30.4