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udpsvd(8)		    System Manager's Manual		     udpsvd(8)

       udpsvd -	UDP/IP service daemon

       udpsvd  [-hpvv]	[-u user] [-l name] [-i	dir|-x cdb] [-t	sec] host port

       udpsvd creates an UDP/IP	socket,	binds it to the	address	host:port, and
       listens on the socket for incoming datagrams.

       If a datagram is	available on the socket, udpsvd	conditionally starts a
       program,	with standard input reading from the socket, and standard out-
       put  redirected	to  standard  error, to	handle this, and possibly more
       datagrams.  udpsvd does not start the program if	another	 program  that
       it  has	started	before still is	running.  If the program exits,	udpsvd
       again listens to	the socket until a  new	 datagram  is  available.   If
       there  are  still  datagrams  available	on  the	socket,	the program is
       restarted immediately.

       udpsvd optionally checks	for special intructions	depending  on  the  IP
       address	or  hostname  of the client sending the	datagram which not yet
       was handled by a	running	program, see ipsvd-instruct(5) for details.

       UDP is a	connectionless protocol.  Most programs	that handle user data-
       grams,  such  as	talkd(8), keep running after receiving a datagram, and
       process subsequent datagrams sent to the	 socket	 until	a  timeout  is
       reached.	  udpsvd  only checks special instructions for a datagram that
       causes a	startup	of the program;	not if a  program  handling  datagrams
       already	is  running.   It  doesn't  make much sense to restrict	access
       through special instructions when using such a program.

       On the  other  hand,  it	 makes	perfectly  sense  with	programs  like
       tftpd(8),  that	fork  to establish a separate connection to the	client
       when receiving the datagram.  In	general	it's adequate to set  up  spe-
       cial instructions for programs that support being run by	tcpwrapper.

       host   host either is a hostname, or a dotted-decimal IP	address, or 0.
	      If host is 0, udpsvd accepts datagrams to	any local IP address.

       port   udpsvd accepts datagrams to host:port.  port may be a name  from
	      /etc/services or a number.

       prog   prog  consists  of  one or more arguments.  udpsvd normally runs
	      prog to handle a datagram, and possibly more, that  is  sent  to
	      the  socket,  if	there is no program that was started before by
	      udpsvd still running and handling	datagrams.

       -i dir read instructions	for handling new connections from the instruc-
	      tions directory dir.  See	ipsvd-instruct(5) for details.

       -x cdb read instructions	for handling new connections from the constant
	      database cdb.  The constant database normally is created from an
	      instructions directory by	running	ipsvd-cdb(8).

       -t sec timeout.	 This  option  only  takes  effect if the -i option is
	      given.  While checking the  instructions	directory,  check  the
	      time of last access of the file that matches the clients address
	      or hostname if any, discard and remove the file if it wasn't ac-
	      cessed  within  the last sec seconds; udpsvd does	not discard or
	      remove a file if the user's write	permission  is	not  set,  for
	      those  files the timeout is disabled.  Default is	0, which means
	      that the timeout is disabled.

       -l name
	      local hostname.  Do not look up the local	hostname in  DNS,  but
	      use  name	 as  hostname.	 By  default udpsvd looks up the local
	      hostname once at startup.

       -u [:]user[:group]
	      drop permissions.	 Set uid and gid to the	user's uid and gid, as
	      found  in	/etc/passwd, before running prog.  If user is followed
	      by a colon and a group, set the gid to group's gid, as found  in
	      /etc/group,  instead  of	user's	gid.   If  group consists of a
	      colon-separated list of group names, set the group  ids  of  all
	      listed  groups.	If user	is prefixed with a colon, the user and
	      all group	arguments are interpreted  as  uid  and	 gids  respec-
	      tively,  and  not	 looked	up in the password or group file.  All
	      supplementary groups are removed.

       -h     Look up the client's hostname in DNS.

       -p     paranoid.	 After looking up the client's hostname	in  DNS,  look
	      up  the  IP  addresses  in DNS for that hostname,	and forget the
	      hostname if none of the addresses	match the client's IP address.
	      You  should  set	this option if you use hostname	based instruc-
	      tions.  The -p option implies the	-h option.

       -v     verbose.	Print verbose messages to standard output.

       -vv    more verbose.  Print more	verbose	messages to standard output.

       ipsvd(7), tcpsvd(8), sslsvd(8), ipsvd-instruct(5), ipsvd-cdb(8)

       Gerrit Pape <>



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