bionic (8) udpsvd.8.gz

Provided by: ipsvd_1.0.0-3.1_amd64 bug

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)