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 https://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   “‐
              https://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 transferred,
              number of clients, etc.)

   Installing
       Go  to  releases  <https://github.com/syncthing/relaysrv/releases>  and  download the file
       appropriate for your operating system. Unpacking it will yield a binary called  strelaysrv
       (or strelaysrv.exe on Windows).  Start this in whatever way you are most comfortable with;
       double clicking should work in any graphical environment. At first start, strelaysrv  will
       generate certificate files and database in the current directory unless given flags to the
       contrary. It will also join the default pools of relays, which means that it  is  publicly
       visible  and any client can connect to it.  The startup message prints instructions on how
       to change this.

       The relay server can also be obtained through  apt,  the  Debian/Ubuntu  package  manager.
       Recent  releases  can be found at syncthing’s apt repository <https://apt.syncthing.net/>.
       The name of the package is syncthing-relaysrv.

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 strelaysrv
          $ sudo mkdir /etc/strelaysrv
          $ sudo chown strelaysrv /etc/strelaysrv
          $ sudo -u strelaysrv /usr/local/bin/strelaysrv -keys /etc/strelaysrv

       This creates a user strelaysrv and a directory /etc/strelaysrv 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 strelaysrv with -ext-address ":443". This tells strelaysrv 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 https://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