XINETD(8) System Manager's Manual XINETD(8)
xinetd - the extended Internet services daemon
xinetd performs the same function as inetd: it starts programs that provide Internet services. Instead of having such servers started at
system initialization time, and be dormant until a connection request arrives, xinetd is the only daemon process started and it listens on
all service ports for the services listed in its configuration file. When a request comes in, xinetd starts the appropriate server.
Because of the way it operates, xinetd (as well as inetd) is also referred to as a super-server.
The services listed in xinetd's configuration file can be separated into two groups. Services in the first group are called multi-threaded
and they require the forking of a new server process for each new connection request. The new server then handles that connection. For
such services, xinetd keeps listening for new requests so that it can spawn new servers. On the other hand, the second group includes ser-
vices for which the service daemon is responsible for handling all new connection requests. Such services are called single-threaded and
xinetd will stop handling new requests for them until the server dies. Services in this group are usually datagram-based.
So far, the only reason for the existence of a super-server was to conserve system resources by avoiding to fork a lot of processes which
might be dormant for most of their lifetime. While fulfilling this function, xinetd takes advantage of the idea of a super-server to pro-
vide features such as access control and logging. Furthermore, xinetd is not limited to services listed in /etc/services. Therefore, any-
body can use xinetd to start special-purpose servers.
-d Enables debug mode. This produces a lot of debugging output, and it makes it possible to use a debugger on xinetd.
This option enables syslog logging of xinetd-produced messages using the specified syslog facility. The following facility names
are supported: daemon, auth, user, local[0-7] (check syslog.conf(5) for their meanings). This option is ineffective in debug mode
since all relevant messages are sent to the terminal.
xinetd-produced messages will be placed in the specified file. Messages are always appended to the file. If the file does not
exist, it will be created. This option is ineffective in debug mode since all relevant messages are sent to the terminal.
Determines the file that xinetd uses for configuration. The default is /etc/xinetd.conf.
The process ID is written to the file. This option is ineffective in debug mode.
Tells xinetd to stay in the foreground rather than detaching itself, to support being run from init or daemontools. This option
automatically sets -stayalive (see below).
Tells xinetd to stay running even if no services are specified.
This option places a limit on the number of concurrently running processes that can be started by xinetd. Its purpose is to prevent
process table overflows.
This option places a limit on the number of concurrently running servers for remote userid acquisition.
This option causes xinetd to print out its version information.
This option causes xinetd to read /etc/inetd.conf in addition to the standard xinetd config files. /etc/inetd.conf is read after
the standard xinetd config files.
This option instructs xinetd to perform periodic consistency checks on its internal state every interval seconds.
The syslog and filelog options are mutually exclusive. If none is specified, the default is syslog using the daemon facility. You should
not confuse xinetd messages with messages related to service logging. The latter are logged only if this is specified via the configuration
xinetd performs certain actions when it receives certain signals. The actions associated with the specific signals can be redefined by
editing config.h and recompiling.
SIGHUP causes a hard reconfiguration, which means that xinetd re-reads the configuration file and terminates the servers for ser-
vices that are no longer available. Access control is performed again on running servers by checking the remote location,
access times and server instances. If the number of server instances is lowered, some arbitrarily picked servers will be
killed to satisfy the limit; this will happen after any servers are terminated because of failing the remote location or
access time checks. Also, if the INTERCEPT flag was clear and is set, any running servers for that service will be termi-
nated; the purpose of this is to ensure that after a hard reconfiguration there will be no running servers that can accept
packets from addresses that do not meet the access control criteria.
SIGQUIT causes program termination.
SIGTERM terminates all running servers before terminating xinetd.
SIGUSR1 causes an internal state dump (the default dump file is /var/run/xinetd.dump; to change the filename, edit config.h and
SIGIOT causes an internal consistency check to verify that the data structures used by the program have not been corrupted. When
the check is completed xinetd will generate a message that says if the check was successful or not.
On reconfiguration the log files are closed and reopened. This allows removal of old log files.
/etc/xinetd.conf default configuration file
default dump file
Panos Tsirigotis, CS Dept, University of Colorado, Boulder Rob Braun
14 June 2001 XINETD(8)