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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



 NAME
      dxpc - Differential X Protocol Compressor


 RELEASE
      3.9.1


 SYNOPSIS
      dxpc [common] [client | server] [connect]

      [common] options are:
           -p port_num -f -k -v -s debug_level -l log_file

      [client] options (valid for CLIENT process) are:
           -i compression_lvl -d display_num -u

      [server] options (valid for SERVER process) are:
           -D display -b(a|w)

      [connect] options are:
           hostname -w

 DESCRIPTION
      dxpc is an X protocol compressor designed to improve the speed of  X11
      applications   run  over  low-bandwidth  links  (such  as  dialup  PPP
      connections).

      dxpc must be run at both ends of a low-bandwidth link.   On  the  host
      where  the real X server is, dxpc runs in "Server Proxy" mode.  On the
      host at the other end of the link, dxpc runs in "Client  Proxy"  mode.
      The  Client  Proxy  dxpc must be started first.  When the Server Proxy
      dxpc is started, it connects to the Client Proxy.  (Note that versions
      of  dxpc before 3.3.1 used the opposite convention.)  If either of the
      two communicating dxpc instances is subsequently terminated, the other
      one automatically shuts down.

      The Client Proxy mimics an X server.  X client applications connect to
      the  Client  Proxy  using  display  "unix:8"  (or "<hostname>:8"; dxpc
      supports both UNIX domain and TCP sockets).  The Client Proxy receives
      X  requests  from  the application, compresses them, and sends them to
      the Server Proxy.  The Server  Proxy  uncompresses  the  requests  and
      sends them to the real X server.  Similarly, the Server Proxy receives
      X events, replies, and errors from the real X server.   It  compresses
      these  messages and sends them to the Client Proxy, which uncompresses
      them and sends them to the client application.

      The compression performance of  dxpc  depends  upon  the  types  of  X
      applications  being run.  For many applications, dxpc achieves between
      3:1 and 6:1 compression of the X protocol traffic.




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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



 MODES
      dxpc has two modes; the connection mode, which is either listening  or
      connecting; and the X mode, which is either client or server.

      The listening process waits for a connecting process to  initiate  the
      TCP  connection  between the two processes. The listening process must
      always  be  started  first.  The  connecting  process  initiates   the
      connection  to  the listening process. dxpc will run as the connecting
      process if a hostname  argument  is  supplied  (see  connect  options,
      above). Otherwise it will run as the listening process.

      The server process is typically located on the  same  machine  as  the
      real  X  server,  and  is  responsible  for  displaying  the output of
      applications. The client process is  typically  located  on  the  same
      machine  as  the X applications, and is responsible for forwarding the
      output of those applications to the server process. By  default,  dxpc
      runs  as the client process if it is the listening process (due to the
      lack of a hostname argument) and the  server  process  if  it  is  the
      connecting process, but the -w switch reverses this.

      For example, the command  dxpc  myhost.work.com  starts  dxpc  as  the
      connecting  process  (because  a host name is supplied) and the server
      process (because it is the connecting process and -w is not supplied).
      The  command  dxpc -w starts dxpc as the listening process (because no
      hostname is supplied) and  the  server  process  (because  it  is  the
      listening process, and -w reverses the usual logic).


 Options
      -b(a|w)     This option specifies that any windows created  should  be
                  created  with  the BackingStore option set to Always (-ba)
                  or WhenMapped (-bw), if the application has  not  set  the
                  option  itself.  Using the BackingStore option will reduce
                  traffic to repaint exposed regions of the window,  at  the
                  cost  of  extra  memory use in the X server itself.  (This
                  option is ignored in Client Proxy mode.)

                  NOTE: The -ba option can cause Expose events  to  be  sent
                  before  the  client  has  mapped  its  windows.   This can
                  confuse some client programs, notably  GNU  Emacs  version
                  20.3.   The  "bug"  in this case is that dxpc shouldn't be
                  setting BackingStore to Always  behind  the  application's
                  back.   Neverless, the option is available, if you want to
                  try it; many client programs still function fine with  it,
                  and  it will cause the contents of iconified windows to be
                  retained.


      -d displaynum
                  This option specifies the number of  the  X  display  that
                  dxpc  imitates.   The default value is 8.  (This option is



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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



                  ignored in Server Proxy mode.)


      -f          This option tells  dxpc  to  fork  and  run  as  a  daemon
                  process.   All  subsequent non-error output is suppressed,
                  including statistics reports.  The daemon can be killed by
                  use of the -k option.


      -k          This option tells dxpc to read a pid from the lockfile  in
                  the  user's  home directory and then send a SIGKILL to the
                  old process.  It does some error checking to try to ensure
                  that  the  file  contains  a  valid  pid file (and nothing
                  else).  The pidfile will exist only if  dxpc  was  started
                  with the -f option.


      -l          This option is used to tell dxpc  to  write  messages  and
                  statistics to a logfile.  Very useful with the -f option.


      -p portnumber
                  This option specifies the TCP port number to be  used  for
                  communication  between  the  Client  Proxy  and the Server
                  Proxy.  The default value is 4000.


      -s(1|2)     Print a report on dxpc's compression performance for an  X
                  application  when  the application exits.  In Client Proxy
                  mode,  dxpc  displays  a  report  on  the  compression  of
                  messages generated by the X client.  In Server Proxy mode,
                  dxpc displays a report  on  the  compression  of  messages
                  generated by the X server.  The -s1 option yields a simple
                  report that provides the overall compression  ratio.   The
                  -s2  option  yields  a  far  more  detailed  report on the
                  compression ratios achieved for all the individual message
                  types  in  the  X protocol.  The -s2 option is the "hacker
                  option"; most people will probably  want  the  -s1  report
                  instead.


      -u -t       Normally, dxpc in Client Proxy mode imitates an X display,
                  :8  by  default, by listening on both a UNIX domain socket
                  and a TCP socket.  The -u option tells it not to  use  the
                  UNIX  domain  port,  and the -t option tells it not to use
                  the TCP port.  (These options are ignored in Server  Proxy
                  mode.)


      -v          This option tells dxpc to print out its version number and
                  copyright message and exit.



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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



      -w          Use of this option swaps the  connection  sequence.   That
                  is, the client will initiate the connection to the server.
                  Thus, instead of starting the client like dxpc -f and  the
                  server  as dxpc -f workserver, you can start the client as
                  dxpc -w -f homepc and the server  as  dxpc  -w  -f.   This
                  option  is  intended  to  be useful for people running the
                  client proxy on a machine behind a firewall.


      hostname    This argument must be used in Server Proxy  mode  to  tell
                  dxpc the hostname or IP address of the machine where other
                  dxpc (the one in Client Proxy  mode)  is  running.   (Note
                  that  the  presence  of this argument is what puts dxpc in
                  Server Proxy mode.  If this argument  is  not  used,  dxpc
                  runs in Client Proxy mode.)


      -D display  Specify X host on which to display  proxied  applications.
                  Defaults to value of the DISPLAY environment variable.


      -i(0..9|99|999)
                  This option controls bitmap image compression. This option
                  is   only   valid  on  the  instance  which  is  accepting
                  connections; usually this is the client, but the -w option
                  will  reverse this, making the -i option valid only on the
                  server. The specified  number  is  the  image  compression
                  level;  higher levels offer better compression at the cost
                  of greater CPU  and  memory  utilization  (mostly  on  the
                  client  proxy). The actual behavior of each level is given
                  below.

                  0  :  No  compression  (except  for   the   very   limited
                  compression  supported  in  dxpc  3.7.0).  In other words,
                  behaves like 3.7.0 (but is incompatible with it)

                  1 : LZO lzo1x_1 compression; very fast, low CPU and memory
                  use, reasonable compression.

                  2-9: LZO lzo1c_... variant compression algorithms. lzo1c_2
                  actually seems to be worse than lzo1x_1...

                  99:  LZO  lzo1c_99  algorithm.  Slow,  but   pretty   good
                  compression.  NB:  I  have  seen  a  couple of unexplained
                  crashes when using this level. Not recommended.

                  999: LZO lzo1x_999 compression. Slow (but fast  enough  to
                  feed  a  128K  ISDN  link  when hosted on a Pentium II/300
                  without maxing out the processor), but  good  compression.
                  This is the default and recommended value.




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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



 EXAMPLES
      Assume that you're running a real X server on the console of  a  local
      workstation   called   homepc,  and  that  you  want  to  run  some  X
      applications on a  remote  system  called  workserver  and  have  them
      display on the console of the local system.

      On workserver, run
           $ export DISPLAY=homepc:0
          $ dxpc -f
          $ export DISPLAY=unix:8

      On homepc, run
          $ export DISPLAY=unix:0
          $ dxpc -f workserver

      Now on workserver,
          $ xterm&
          $ xemacs&
          etc...


 DXPC AND XAUTH
      If you use X authorization, with a .Xauthority file on the workstation
      where  your  real  X  server runs, you'll need to set up a .Xauthority
      file on the host where the ClientProxy runs.  One way to do this is:

      Copy your ~/.Xauthority file from the host where  the  real  X  server
      runs to the host where the Client Proxy runs.

      Run
          xauth list
      to see the authorization keys.  There should be one for  your  real  X
      display.  It will look something like this:
          <hostname>/unix:0   MIT-MAGIC-COOKIE-1   <hex string>
      On the host where the Client Proxy is located, add a new entry to  the
      .Xauthority  file  with  the  display  name  of the fake X server (the
      DISPLAY where the Client Proxy is listening)  and  all  of  the  other
      values from the entry for the real X display.  The xauth "add" command
      can be used, like this:
          xauth add <hostname>/unix:8 MIT-MAGIC-COOKIE-1  <hex string>
      where <hostname> is the name of the host where  the  Client  Proxy  is
      running  and  <hex  string>  has  the  same  value as the <hex string>
      obtained for the real X display in step 2.   Once  you  do  this,  you
      should be able to run X clients through dxpc successfully.



 TROUBLESHOOTING
      Some windows don't appear. This can happen if the -ba option is  used,
      and a client program (such as GNU Emacs version 20.3) does not request
      backing store and thus assumes  that  Expose  events  imply  that  the



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 DXPC(1)                            dxpc                             DXPC(1)
                              February 2, 2007



      window  has  been  mapped.   Use  -bw,  or  leave  out  the  -b option
      altogether.

      No windows appear. This can happen if you are using a newer version of
      dxpc  with  an older one, from before the client and server roles were
      changed.  A connection can be established between them, but both sides
      believe  themselves  to  be  the  client  side,  or both sides believe
      themselves to be the server side.  Make sure  you're  using  the  same
      version of dxpc at both ends of the connection.


 AUTHOR
      Brian Pane


 MAINTAINER
      Kevin Vigor (kevin@vigor.nu)


 ACKNOWLEDGMENTS
      dxpc has adopted many  good  ideas  from  the  HBX  and  FHBX  systems
      (http://www.cs.dartmouth.edu/~jmd/decs/DECSpage.html).

      Thanks to all of the users of dxpc who have contributed  feedback  and
      suggestions.


 SEE ALSO
      xauth(1), README file from dxpc distribution

























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