Red Hat Bugzilla – Bug 426242
Slow reactivity of vnc server
Last modified: 2013-04-30 19:37:53 EDT
Description of problem:
vnc server has sometimes slow response to some key typing and/or mouse click.
This is not related to a network problem: it happens even when using a local
client connecting to localhost.
The reactivity delay can be up to 5 seconds and the problem seems to occur
randomly (but with high probability rate).
Version-Release number of selected component (if applicable):
Seems random, but easy to reproduce by working a few seconds from a vnc client.
Steps to Reproduce:
1. Start a vnc server
2. Connect to it from any client/OS/host
3. Start working...: you will soon find it very uncomfortable !
As expected, but slow.
_ Sometimes the screen refresh is slow (even when vnc is connected thru
_ This might be related: when starting wireshark from vnc, the plugin scan at
startup lasts more than 5 minutes, displaying each plugin name very slowly.
1. From vnc, type xhost + in a terminal
2. Start wireshark from the menu, entering the root password if needed.
The problem does not occur when connecting to non-fedora8 vnc-servers using the
same clients as those used for the above mentioned tests.
Hm, I'm not able reproduce this one. Do you have specific configuration? I
simply installed and started vnc server and it works as expected.
The configuration I use is dynamic vnc:
_ XDMCP enabled
_ File /etc/xinetd.d/vnc-1024x768x24
socket_type = stream
wait = no
user = root
log_on_failure += USERID
server = /usr/bin/Xvnc
server_args = -inetd -once -query localhost -geometry 1024x768 -dpi 100 -depth
24 -securitytypes=none -render
disable = no
_ Add "vnc-1024x768x24 5926/tcp" to /etc/services
_ Connect with "vncviewer host:26"
... but I also have the same problem when starting a static server manually
Clicking and moving the mouse around, as well as typing ahead improve response.
It seems there is some output buffering that is not flushed when no input event
This problem occurs on ALL installations I've made, regardless of hardware
and/or other configuration or specific computer use.
I found a way to reproduce: the following recipe exhibits the above case with a
_ Start a vnc session, make sure meld package is installed (yum install meld)
_ In this session, compare two text files of at least 100 lines (some of them
~80 chars) using meld
_ Inside meld, make some changes to a file, move cursor around, some other
changes, press shift, release it, etc. watch the reactivity to key pressure...
although very few screen changes are required, the response time to key
pressures may be up to several seconds ! This makes edition almost impossible
and does not occur on a regular X server. I'm still working on a 100MHz,
uncongestioned ethernet LAN, without any router between the client and the
_ If you're still not convinced, try resizing the meld window some xy tiny
pixels and note the refresh time... as already said, moving the mouse around
improves the reactivity !
I also reproduce this behavior with the same probability with a (non-
opensourced, non-packaged) html editor written in java called "Arachnophilia"
I hope this helps.
Many thanks for your attention
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Seems to be fixed in F10. Closing bug.