SLAC National Accelerator Laboratory

SLAC Linux Frequently Asked Questions

SLAC Computing
Linux at SLAC
Updated: 10 May 2006

Can I install a more current version of MySQL?

Red Hat ships a version of MySQL, but some users wish to use a more current version downloaded from the Web site. If you do, though, be sure to install the "shared compatibility libraries" (the MySQL-shared-compat RPM) rather than the standard "shared libraries" (MySQL-shared-standard). A number of MySQL-related RPMs, such as MySQL-python, have dependencies on the older versions of the MySQL shared libraries which are not included in MySQL-shared-standard. A security update to one of these ancillary RPMs can trigger a re-installation of Red Hat's version of the libraries which, in turn, can end up un-installing all or part of MySQL-shared-standard. The MySQL-shared-compat RPMs includes these older shared libraries and thus satisfies the dependencies, preventing this kind of problem.

Why won't my Paw (or ROOT) window refresh?

Backing store is a mechanism that an X server may use to refresh a portion of a window after another window has temporarily obscured it. It is intended to improve performance by handling such refreshes locally in the X server, without incurring network overhead to talk to the client and, possibly, significant recalculation in the client to reconstruct the contents of the window. However, there are mixed opinions as to whether the use of backing store, as defined for X servers, is likely to improve or degrade performance; see, for example, Why doesn't my X server use backing store? How can I turn it on?.

Clients are not supposed to depend on tha availability of backing store in the X server -- not only is it supposed to be an optional and configurable feature, but some servers might not have sufficient memory to handle all the backing store requests. Nevertheless, some clients do depend on it, including Paw and ROOT.

There is no documented way in the current version of XFree86 (4.3) to force the X server to use backing store for all windows; however, there is an undocumented command-line option, +bs that seems to have this effect (the documented -bs option disables backing store). If you need to use an application that's not redrawing its windows after another window obscures them, you can try configuring your system to start your X server with the +bs command-line option. See How can I modify my X server options? for instructions on specifying command line options for your X server.

How can I modify my X server options?


If you are using gdm (the GNOME Display Manager), the relevant configuration file is /etc/X11/gdm/gdm.conf. Edit this file as root and find the stanza beginning with a line like this:

Find the command= line within this stanza and append or modify your options to the command line.

The gdm daemon only rereads its config file when it first starts or when you send it a HUP signal (which has the side effect of restarting killing your current gdm session). Thus, it is not sufficient to simply logout and login again to get your X server running with its new options. One solution is to simply reboot your machine. Here's a somewhat less disruptive solution.

  • Logout from your current gdm session.
  • Press CTRL-ALT-F2 (say) to get to one of the command-line login screens, and login in line mode.
  • Issue the command, ps -ef | grep gdm and find the process id (pid) for the primary gdm daemon. This is the gdm instance whose parent process has pid=1.
  • Issue the command kill -HUP gdm-pid where gdm-pid is the process id of the primary gdm daemon.
  • After a short wait your X server should restart and you should be presented with a login screen. Before logging into your gdm session, you should first go back to your login screen by pressing CTRL-ALT-F2 and logout. (Before logging out, you might was to do ps -ef | grep X and check that the X server is now running with your options.)
  • Press CTRL-ALT-F7 (or possibly CTRL-ALT-F8) to get back to your gdm login screen. (I have sometimes seen this screen refuse to refresh; if that happens, try CTRL-ALT-BS to restart the X server yet again.

If you are using kdm (the KDE display manager), you should first search the file /etc/kde/kdm/kdmrc for a line beginning "Xservers=". Normally, this line will point to a file such as /usr/share/config/kdm/Xservers, which usually resolves to /etc/X11/xdm/Xservers. This file will normally contain a single, non-comment line that looks something like this:

  :0 local /usr/X11R6/bin/X
Edit this file as root and append or modify your options following the path to the Xserver binary.

To restart your X server, logout of your kdm session and login again. Use the command ps -ef | grep X

to verify that your X server is now running with your desired options.
Len Moss