dxpc - Differential X Protocol Compressor
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:
dxpc is an X protocol compressor designed to improve the speed of X11
applications run over low-bandwidth links (such as dialup PPP
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.
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).
-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
This option specifies the number of the X display that dxpc
imitates. The default value is 8. (This option is 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 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
-l This option is used to tell dxpc to write messages and
statistics to a logfile. Very useful with the -f option.
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
-v This option tells dxpc to print out its version number and
copyright message and exit.
-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.
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.
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,
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.
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.
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 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.
Kevin Vigor (firstname.lastname@example.org)
dxpc has adopted many good ideas from the HBX and FHBX systems
Thanks to all of the users of dxpc who have contributed feedback and
xauth(1), README file from dxpc distribution