NAME
xinetd - the extended Internet services daemon
SYNOPSIS
xinetd [options]
DESCRIPTION
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 services 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 provide features such as access control and logging. Furthermore, xinetd is not limited to services listed in /etc/services. Therefore, anybody can use xinetd to start special-purpose servers.
OPTIONS
-d Enables debug mode. This produces a lot of debugging output, and
it makes it possible to use a debugger on xinetd.
-syslog syslog_facility
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.
-filelog logfile
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.
-f config_file
Determines the file that xinetd uses for configuration. The
default is /etc/xinetd.conf.
-pidfile pid_file
The process ID is written to the file. This option is
ineffective in debug mode.
-dontfork
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).
-stayalive
Tells xinetd to stay running even if no services are specified.
-limit proc_limit
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.
-logprocs limit
This option places a limit on the number of concurrently running
servers for remote userid acquisition.
-version
This option causes xinetd to print out its version information.
-inetd_compat
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.
-cc interval
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
file.
CONTROLLING XINETD
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 services 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 terminated; 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 recompile).
SIGABRT 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.
FILES
/etc/xinetd.conf default configuration file
/var/run/xinetd.dump
default dump file
ENVIRONMENT
REMOTE_HOST Contains the IP address of the client.
SEE ALSO
inetd(8), xinetd.conf(5), xinetd.log(5) http://cr.yp.to/daemontools.html
AUTHOR
Panos Tsirigotis, CS Dept, University of Colorado, Boulder Rob Braun
PRONUNCIATION
zy-net-d
14 June 2001 XINETD(8)
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