+
+
+s6-networking
+Software
+skarnet.org
+
+
+ The s6-ipcserverd program
+
+
+s6-ipcserverd is the serving part of the
+s6-ipcserver super-server.
+It assumes that its stdin is a bound and listening Unix
+domain socket, and
+it accepts connections from clients connecting to it, forking a
+program to handle each connection.
+
+
+ Interface
+
+
+ s6-ipcserverd [ -1 ] [ -v verbosity ] [ -P | -p ] [ -c maxconn ] [ -C localmaxconn ] prog...
+
+
+
+ - s6-ipcserverd accepts connections from clients to an already
+bound and listening SOCK_STREAM Unix domain socket which is its
+standard input.
+ - For every client connection to this socket, it
+forks. The child sets some environment variables, then
+executes prog... with stdin reading from the socket and
+stdout writing to it.
+ - Depending on the verbosity level, it logs what it does to stderr.
+ - It runs until killed by a signal. Depending on the received
+signal, it may kill its children before exiting.
+
+
+ Environment variables
+
+
+ For each connection, an instance of prog... is spawned with
+the following variables set:
+
+
+
+ - PROTO: always set to IPC
+ - IPCREMOTEEUID: set to the effective UID of the client,
+unless credentials lookups have been disabled
+ - IPCREMOTEEGID: set to the effective GID of the client,
+unless credentials lookups have been disabled
+ - IPCREMOTEPATH: set to the path associated with the remote socket,
+if any. Be aware that it may contain arbitrary characters.
+ - IPCCONNNUM: set to the number of connections originating from
+the same user (i.e. same uid)
+
+
+
+ If client credentials lookup has been disabled, IPCREMOTEEUID and
+IPCREMOTEEUID will be set, but empty.
+
+
+
+ Options
+
+
+ - -1 : write a newline to stdout, and close stdout,
+right before entering the client-accepting loop.
+If stdout is suitably redirected, this can be used by monitoring
+programs to check when the server is accepting connections.
+The s6-notifywhenup
+program can be used before the s6-ipcserver
+invocation to notify listeners when the server is ready.
+ - -v verbosity : be more or less
+verbose. verbosity can be 0 (quiet), 1 (normal), or 2
+(verbose).
+ - -P : disable client credentials lookups. The
+IPCREMOTEEUID and IPCREMOTEEGID environment variables will be unset
+in every instance of prog.... This is the portable option,
+because not every system supports credential lookup across Unix domain
+sockets; but it is not as secure.
+ - -p : enable client credentials lookups. This
+is the default; it works at least on Linux, Solaris, and
+*BSD systems. On systems that do not support it, every connection
+attempt will fail with a warning message.
+ - -c maxconn : accept at most
+maxconn concurrent connections. Default is 40. It is
+impossible to set it higher than 1000.
+ - -C localmaxconn : accept at most
+localmaxconn connections from the same user ID.
+Default is 40. It is impossible to set it higher than maxconn.
+
+
+ Signals
+
+
+ - SIGTERM: exit.
+ - SIGHUP: send a SIGTERM and a SIGCONT to all children.
+ - SIGQUIT: send a SIGTERM and a SIGCONT to all children, then exit.
+ - SIGABRT: send a SIGKILL to all children, then exit.
+
+
+ Notes
+
+
+ - Unlike his close cousin
+ipcserver,
+s6-ipcserverd does not perform operations such as access control. Those are
+delegated to the
+s6-ipcserver-access program.
+ - s6-ipcserverd can be used to set up
+local services.
+ - s6-ipcserverd is meant to be execve'd into by a program that gets
+the listening socket. That program is normally
+s6-ipcserver-socketbinder,
+which creates the socket itself; but it can be a different one if the
+socket is to be retrieved by another means, for instance by fd-passing
+from a fd-holding daemon (some people call this "socket activation").
+
+
+
+