Linux cli command systemd-socket-proxyd

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NAME 🖥️ systemd-socket-proxyd 🖥️

socket-proxyd - Bidirectionally proxy local sockets to another (possibly remote) socket

SYNOPSIS

systemd-socket-proxyd [OPTIONS…] HOST:PORT

systemd-socket-proxyd [OPTIONS…] UNIX-DOMAIN-SOCKET-PATH

DESCRIPTION

systemd-socket-proxyd is a generic socket-activated network socket forwarder proxy daemon for IPv4, IPv6 and UNIX stream sockets. It may be used to bi-directionally forward traffic from a local listening socket to a local or remote destination socket.

One use of this tool is to provide socket activation support for services that do not natively support socket activation. On behalf of the service to activate, the proxy inherits the socket from systemd, accepts each client connection, opens a connection to a configured server for each client, and then bidirectionally forwards data between the two.

This utilitys behavior is similar to socat(1). The main differences for systemd-socket-proxyd are support for socket activation with “Accept=no” and an event-driven design that scales better with the number of connections.

Note that systemd-socket-proxyd will not forward socket side channel information, i.e. will not forward SCM_RIGHTS, SCM_CREDENTIALS, SCM_SECURITY, SO_PEERCRED, SO_PEERPIDFD, SO_PEERSEC, SO_PEERGROUPS and similar.

OPTIONS

The following options are understood:

-h, –help

Print a short help text and exit.

–version

Print a short version string and exit.

–connections-max=, -c

Sets the maximum number of simultaneous connections, defaults to 256. If the limit of concurrent connections is reached further connections will be refused.

Added in version 233.

–exit-idle-time=

Sets the time before exiting when there are no connections, defaults to infinity. Takes a unit-less value in seconds, or a time span value such as “5min 20s”.

Added in version 246.

EXIT STATUS

On success, 0 is returned, a non-zero failure code otherwise.

EXAMPLES

Simple Example

Use two services with a dependency and no namespace isolation.

Example 1. proxy-to-nginx.socket

[Socket] ListenStream=80

[Install]
WantedBy=sockets.target

Example 2. proxy-to-nginx.service

[Unit] Requires=nginx.service After=nginx.service Requires=proxy-to-nginx.socket After=proxy-to-nginx.socket

[Service]
Type=notify
ExecStart=/usr/lib/systemd/systemd-socket-proxyd /run/nginx/socket
PrivateTmp=yes
PrivateNetwork=yes

Example 3. nginx.conf

[…] server { listen unix:/run/nginx/socket; […]

Example 4. Enabling the proxy

systemctl enable –now proxy-to-nginx.socket

$ curl http://localhost:80/

If nginx.service has StopWhenUnneeded= set, then passing –exit-idle-time= to systemd-socket-proxyd allows both services to stop during idle periods.

Namespace Example

Similar as above, but runs the socket proxy and the main service in the same private namespace, assuming that nginx.service has PrivateTmp= and PrivateNetwork= set, too.

Example 5. proxy-to-nginx.socket

[Socket] ListenStream=80

[Install]
WantedBy=sockets.target

Example 6. proxy-to-nginx.service

[Unit] Requires=nginx.service After=nginx.service Requires=proxy-to-nginx.socket After=proxy-to-nginx.socket JoinsNamespaceOf=nginx.service

[Service]
Type=notify
ExecStart=/usr/lib/systemd/systemd-socket-proxyd 127.0.0.1:8080
PrivateTmp=yes
PrivateNetwork=yes

Example 7. nginx.conf

[…] server { listen 8080; […]

Example 8. Enabling the proxy

systemctl enable –now proxy-to-nginx.socket

$ curl http://localhost:80/

SEE ALSO

systemd(1), systemd.socket(5), systemd.service(5), systemctl(1), socat(1), nginx(1), curl(1)

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