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)