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



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.  Switch user ID to user's UID, and group ID to
              user's primary GID after creating and binding to the socket.  If
              user is followed by a colon and a group name, the group ID is
              switched to the GID of group instead.  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)
