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       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
       output  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
       datagrams,  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
       special 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
              instructions  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
              accessed 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
              respectively, 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
              instructions.  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 <>