systemd-ssh-generator — Generator for binding a socket-activated SSH server to local AF_VSOCK
and AF_UNIX sockets
/usr/lib/systemd/system-generators/systemd-ssh-generator
systemd-ssh-generator binds a socket-activated SSH server to local
AF_VSOCK and AF_UNIX sockets under certain conditions. It only
has an effect if the sshd(8) binary is
installed. Specifically, it does the following:
If invoked in a VM with AF_VSOCK support, a socket-activated SSH
per-connection service is bound to AF_VSOCK port 22.
If invoked in a container environment with a writable directory
/run/host/unix-export/ pre-mounted it binds SSH to an AF_UNIX
socket /run/host/unix-export/ssh. The assumption is that this directory is bind
mounted to the host side as well, and can be used to connect to the container from there. See Container Interface for more information about
this interface.
A local AF_UNIX socket
/run/ssh-unix-local/socket is also bound, unconditionally. This may be used for
SSH communication from the host to itself, without involving networking, for example to traverse
security boundaries safely and with secure authentication.
Additional AF_UNIX and AF_VSOCK sockets are
optionally bound, based on the systemd.ssh_listen= kernel command line option or the
ssh.listen system credential (see below).
See systemd-ssh-proxy(1) for details on how to connect to these sockets via the ssh client.
The ssh.authorized_keys.root credential can be used to allow specific public keys
to log in over SSH. See
systemd.system-credentials(7)
for more information.
The generator will use a packaged sshd@.service service template file if one
exists, and otherwise generate a suitable service template file.
systemd-ssh-generator implements
systemd.generator(7).
systemd-ssh-generator understands the following
kernel-command-line(7)
parameters:
systemd.ssh_auto=¶This option takes an optional boolean argument, and defaults to yes. If enabled, the
automatic binding to the AF_VSOCK and AF_UNIX sockets
listed above is done. If disable, this is not done, except for those explicitly requested via
systemd.ssh_listen= on the kernel command line or via the
ssh.listen system credential.
systemd.ssh_listen=¶This option configures an additional socket to bind SSH to. It may be used multiple
times to bind multiple sockets. The syntax should follow the one of ListenStream=,
see
systemd.socket(5)
for details. This functionality supports all socket families systemd supports, including
AF_INET and AF_INET6.
systemd-ssh-generator supports the system credentials logic. The following credentials are used when passed in:
ssh.listen¶This credential should be a text file, with each line referencing one additional
socket to bind SSH to. The syntax should follow the one of ListenStream=, see
systemd.socket(5)
for details. This functionality supports all socket families systemd supports, including
AF_INET and AF_INET6.