Ubuntu Manpage: xinetd - the extended Internet services daemon

Provided by: xinetd_2.3.15.4-3build1_amd64

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.

AUTHOR

       Panos Tsirigotis, CS Dept, University of Colorado, Boulder Rob Braun

PRONUNCIATION

       zy-net-d

                                                  14 June 2001                                         XINETD(8)