Provided by: syncthing-relaysrv_1.1.4~ds1-4ubuntu1.2_amd64 
NAME
strelaysrv - Syncthing Relay Server
SYNOPSIS
strelaysrv [-debug] [-ext-address=<address>] [-global-rate=<bytes/s>] [-keys=<dir>] [-listen=<listen addr>]
[-message-timeout=<duration>] [-nat] [-nat-lease=<duration> [-nat-renewal=<duration>]
[-nat-timeout=<duration>] [-network-timeout=<duration>] [-per-session-rate=<bytes/s>]
[-ping-interval=<duration>] [-pools=<pool addresses>] [-protocol=<string>] [-provided-by=<string>]
[-status-srv=<listen addr>]
DESCRIPTION
Syncthing relies on a network of community-contributed relay servers. Anyone can run a relay server, and
it will automatically join the relay pool and be available to Syncthing users. The current list of relays
can be found at http://relays.syncthing.net/.
OPTIONS
-debug Enable debug output.
-ext-address=<address>
An optional address to advertising as being available on. Allows listening on an unprivileged port
with port forwarding from e.g. 443, and be connected to on port 443.
-global-rate=<bytes/s>
Global rate limit, in bytes/s.
-keys=<dir>
Directory where cert.pem and key.pem is stored (default “.”).
-listen=<listen addr>
Protocol listen address (default “:22067”).
-message-timeout=<duration>
Maximum amount of time we wait for relevant messages to arrive (default 1m0s).
-nat Use UPnP/NAT-PMP to acquire external port mapping
-nat-lease=<duration>
NAT lease length in minutes (default 60)
-nat-renewal=<duration>
NAT renewal frequency in minutes (default 30)
-nat-timeout=<duration>
NAT discovery timeout in seconds (default 10)
-network-timeout=<duration>
Timeout for network operations between the client and the relay. If no data is received between
the client and the relay in this period of time, the connection is terminated. Furthermore, if no
data is sent between either clients being relayed within this period of time, the session is also
terminated. (default 2m0s)
-per-session-rate=<bytes/s>
Per session rate limit, in bytes/s.
-ping-interval=<duration>
How often pings are sent (default 1m0s).
-pools=<pool addresses>
Comma separated list of relay pool addresses to join (default “‐
http://relays.syncthing.net/endpoint”). Blank to disable announcement to a pool, thereby remaining
a private relay.
-protocol=<string>
Protocol used for listening. ‘tcp’ for IPv4 and IPv6, ‘tcp4’ for IPv4, ‘tcp6’ for IPv6 (default
“tcp”).
-provided-by=<string>
An optional description about who provides the relay.
-status-srv=<listen addr>
Listen address for status service (blank to disable) (default “:22070”). Status service is used
by the relay pool server UI for displaying stats (data transfered, number of clients, etc.)
SETTING UP
Primarily, you need to decide on a directory to store the TLS key and certificate and a listen port. The
default listen port of 22067 works, but for optimal compatibility a well known port for encrypted traffic
such as 443 is recommended. This may require additional setup to work without running as root or a
privileged user, see Running on port 443 as an unprivileged user below. In principle something similar to
this should work on a Linux/Unix system:
$ sudo useradd relaysrv
$ sudo mkdir /etc/relaysrv
$ sudo chown relaysrv /etc/relaysrv
$ sudo -u relaysrv /usr/local/bin/relaysrv -keys /etc/relaysrv
This creates a user relaysrv and a directory /etc/relaysrv to store the keys. The keys are generated on
first startup. The relay will join the global relay pool, unless a -pools="" argument is given.
To make the relay server start automatically at boot, use the recommended procedure for your operating
system.
Client configuration
Syncthing can be configured to use specific relay servers (exclusively of the public pool) by adding the
required servers to the Sync Protocol Listen Address field, under Actions and Settings. The format is as
follows:
relay://<host name|IP>[:port]/?id=<relay device ID>
For example:
relay://private-relay-1.example.com:443/?id=ITZRNXE-YNROGBZ-HXTH5P7-VK5NYE5-QHRQGE2-7JQ6VNJ-KZUEDIU-5PPR5AM
The relay’s device ID is output on start-up.
Running on port 443 as an unprivileged user
It is recommended that you run the relay on port 443 (or another port which is commonly allowed through
corporate firewalls), in order to maximise the chances that people are able to connect. However, binding
to ports below 1024 requires root privileges, and running a relay as root is not recommended. Thankfully
there are a couple of approaches available to you.
One option is to run the relay on port 22067, and use an iptables rule to forward traffic from port 443
to port 22067, for example:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -j REDIRECT --to-port 22067
Or, if you’re using ufw, add the following to /etc/ufw/before.rules:
*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -i eth0 -p tcp --dport 443 -j REDIRECT --to-port 22067
COMMIT
You will need to start relaysrv with -ext-address ":443". This tells relaysrv that it can be contacted on
port 443, even though it is listening on port 22067. You will also need to let both port 443 and 22067
through your firewall.
Another option is described here <https://wiki.apache.org/httpd/NonRootPortBinding>, although your
mileage may vary.
FIREWALL CONSIDERATIONS
The relay server listens on two ports by default. One for data connections and the other for providing
public statistics at http://relays.syncthing.net/. The firewall, such as iptables, must permit incoming
TCP connections to the following ports:
• Data port: 22067/tcp overridden with -listen and advertised with -ext-address
• Status port: 22070/tcp overridden with -status-srv
Runtime iptables rules to allow access to the default ports:
iptables -I INPUT -p tcp --dport 22067 -j ACCEPT
iptables -I INPUT -p tcp --dport 22070 -j ACCEPT
Please consult Linux distribution documentation to persist firewall rules.
SEE ALSO
syncthing-relay(7), syncthing-faq(7), syncthing-networking(7)
AUTHOR
The Syncthing Authors
COPYRIGHT
2014-2019, The Syncthing Authors