Table of Contents
xinetd - the extended Internet services daemon
xinetd [options]
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.
- -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 sys_log.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.
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 run_ning
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 con_fig.h
and recompile).
- 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
/var/run/xinetd.dump
default dump file
inetd(8),
xinetd.conf(5),
xinetd.log(5)
http://cr.yp.to/daemontools.html
Panos Tsirigotis, CS Dept, University of Colorado, Boulder Rob Braun
zy-net-d
Table of Contents