Library - Xen - Solutions to common problems

Sometimes problems may occur, but it may be dependent on the environment.  Common solutions that I've discovered are documented here to save you time in case you encounter them as well.

Can't login to the Dom0 (via login, ssh, ftp, samba, etc.), but the DomU continues to function

If you look at your system console, you may see errors regarding insufficient file handles.  For this problem, the solution is to add the following directive to your /etc/sysctl.conf file:

kern.maxfiles=10000

Remember to change the number 10000 to something greater than the current value (I usually multiply the current value by 3 to 4 times).  Use the "sysctl kern.maxfiles" shell command to view the current setting.

Note:  The "/etc/rc.d/sysctl restart" command will update your kernel settings immediately if you aren't planning to reboot your system.

Errors appear during boot of non-Xen kernel

When booting with a kernel that wasn't compiled for DOM0 mode under Xen, errors appear indicating that "xend" and "xenbackendd" could not be started.  This can be corrected so that the Xen daemons will only be started when Xen can be reliably detected, by modifying "/etc/rc.conf" to appear like the following lines of text:

# Start Xen only when kernel support is present
#
if [ "`/usr/pkg/bin/xen-detect`" != "Not running on Xen." ]; then
  xend=YES
  xenbackendd=YES
  #xendomains=""
else
  xend=NO
  xenbackendd=NO
fi

Although this is not a serious problem, it may be interesting to System Administrators who strive for perfection.

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