NAME

       udpsvd - UDP/IP service daemon

SYNOPSIS

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

DESCRIPTION

       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.

   ATTENTION:
       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.

OPTIONS

       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.

SEE ALSO

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

       http://smarden.org/ipsvd/

AUTHOR

       Gerrit Pape <pape@smarden.org>

                                                                                        udpsvd(8)