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skd - a lightweight socket daemon ================================= skd is a small daemon which binds to a udp, tcp or unix-domain socket, waits for connections and runs a specified program to handle them. It is ideal as a secure, efficient replacement for traditional inetd as well as being an easy-to-use tool for non-privileged users wanting to run their own network services. Datagram and stream sockets are available in both the internet and unix namespaces, each with the expected inetd behaviour. In the internet domain, IPv6 is supported in addition to IPv4. skd also supports connection limits, verbose logging of connections, dropping of privileges, forking into the background with a pidfile and redirecting stderr to syslog or a file. Some of these facilities (such as forking into the background, privilege dropping and logging) are also useful for standalone, non-network services and can be used without binding any socket. Building and installing ----------------------- Unpack the source tar.gz file and change to the unpacked directory. Run 'make', then 'make install' to install in /bin. Alternatively, you can set DESTDIR and/or BINDIR to install in a different location, or strip and copy the compiled skd binary into the correct place manually. skd was developed on GNU/Linux and FreeBSD, but should be reasonably portable. In particular, it is expected to compile on most modern unix platforms. Please report any problems or bugs to Chris Webb <email@example.com>. Usage ----- Usage: skd [OPTIONS] PROG [ARGS]... Options: -i [INTERFACE:]PORT bind a listening socket in the internet namespace -l PATH, -x PATH bind a listening socket in the local unix namespace -s create a stream socket (default socket style) -d create a datagram socket instead of a stream socket -t [INTERFACE:]PORT create a TCP socket: equivalent to -s -i -u [INTERFACE:]PORT create a UDP socket: equivalent to -d -i -b BACKLOG set the listen backlog for a stream socket -c MAXCLIENTS set the maximum number of concurrent connections accepted by a stream socket (default is unlimited) -n set TCP_NODELAY to disable Nagle's algorithm for TCP stream connections -v report information about every connection accepted or initial datagram received to stderr or the log -B fork, establish new session id, redirect stdin and stdout to/from /dev/null if they are attached to a terminal, and run as a daemon in the background -L TAG[:FAC.PRI] start a logger subprocess, redirecting stderr to the system log with tag TAG, facility FAC and priority PRI (defaulting to daemon.notice if unspecified) -L >LOGFILE redirect stderr to create and write to LOGFILE -L >>LOGFILE redirect stderr to append to LOGFILE -P PIDFILE write pid to PIDFILE (after forking if used with -B) -U after binding the socket, drop privileges to those specified by $UID and $GID, and if $ROOT is set, chroot into that directory When a stream socket is specified, listen on it and accept all incoming connections, executing the given program in a child process with stdin and stdout attached to the connection socket. Do not wait for the child to exit before accepting another connection on the listening socket. When a datagram socket is specified, wait for an initial datagram to arrive before launching the given program with stdin and stdout attached to the listening socket. Until this program exits, don't attempt to check for more datagrams or spawn another child. If none of -i, -l, -u is used, no socket is bound and the given program is executed immediately, after any background, logging, pidfile and privilege dropping actions have been completed. This allows use of these facilities for standalone and non-network services. Examples -------- A unix domain echo server running in the foreground, reporting connections to stderr: skd -vl /dev/cat.sock cat An motd server running in the background with a pidfile /var/run/motd.pid, reporting connections to syslog with tag 'testsrv', facility 'daemon' and priority 'info': skd -vt 3000 -BP /var/run/motd.pid -L testsrv:daemon.info \ cat /etc/motd Uwe Ohse's uscheduled running in the background, logging errors from stderr to syslog: skd -BL uschedule:daemon.notice -- uscheduled -d /var/lib/uschedule The last example demonstrates how skd can be useful as a daemontools replacement in a more standard unix environment. I use it to daemonise uschedule, dnscache and tinydns with logs sent to syslog. Copying ------- skd was written by Chris Webb <firstname.lastname@example.org> and is distributed as Free Software under the terms of the MIT license in COPYING.