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NAME

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

SYNOPSIS

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]

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

nbdkit ssh host=ssh.example.com disk.img

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.

nbdkit ssh host=ssh.example.com disk.img user=bob

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

PARAMETERS

compression=true

Enable compression. You should only use this on slow or bandwidth-limited connections. On fast connections it will slow things down.

config=CONFIG_FILE

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.

config=

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.

create=true

(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.

create-mode=MODE

(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.

create-size=SIZE

(nbdkit ≥ 1.32)

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

host=HOST

Specify the name or IP address of the remote host.

This parameter is required.

identity=FILENAME

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.

known-hosts=FILENAME

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.

password=PASSWORD

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.

password=-

Ask for the password (interactively) when nbdkit starts up.

password=+FILENAME

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.

password=-FD

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).

port=PORT

Specify the SSH protocol port name or number.

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

timeout=SECS

Set the SSH connection timeout in seconds.

user=USER

Specify the remote username.

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

verify-remote-host=true
verify-remote-host=false

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:

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.

"%%"

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:

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-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 Red Hat

LICENSE

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

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.