Chapter 27. Troubleshooting Red Hat Virtualization

This chapter covers essential concepts to assist you in troubleshooting problems in Red Hat Virtualization. Troubleshooting topics covered in this chapter include:

troubleshooting tools for Linux and virtualization.
troubleshooting techniques for identifying problems.
The location of log files and explanations of the information in logs.

This chapter is to give you, the reader, a background to identify where problems with virtualization technologies are. Troubleshooting takes practice and experience which are difficult to learn from a book. It is recommended that you experiment and test virtualization on Red Hat Enterprise Linux to develop your troubleshooting skills.

If you cannot find the answer in this document there may be an answer online from the virtualization community. Refer to Section B.1, “Online resources” for a list of Linux virtualization websites.

27.1. Debugging and troubleshooting Red Hat Virtualization

This section summarizes the System Administrator applications, the networking utilities, and the Advanced Debugging Tools (for more information on using these tools to configure the Red Hat Virtualization services, see the respective configuration documentation). You can employ these standard System Administrator Tools and logs to assist with troubleshooting:

Useful commands and applications for troubleshooting

xentop: xentop displays real-time information about a host system and the guest domains.
xm: Using the dmesg and log

vmstat
iostat
lsof

The iostat, mpstat and sar commands are all provided by the sysstat package.

You can employ these Advanced Debugging Tools and logs to assist with troubleshooting:

XenOprofile
systemtap
crash
sysrq
sysrq t
sysrq w

These networking tools can assist with troubleshooting virtualization networking problems:

ifconfig
tcpdump
The tcpdump command 'sniffs' network packets. tcpdump is useful for finding network abnormalities and problems with network authentication. There is a graphical version of tcpdump named wireshark.

brctl

brctl is a networking tool that inspects and configures the Ethernet bridge configuration in the Virtualization linux kernel. You must have root access before performing these example commands:

# brctl show 

bridge-name    bridge-id          STP  enabled  interfaces  
-----------------------------------------------------------------------------
xenbr0             8000.feffffff       no        vif13.0
xenbr1             8000.ffffefff       yes       pddummy0
xenbr2             8000.ffffffef       no        vif0.0

# brctl showmacs xenbr0

port-no           mac-addr                  local?       aging timer

1                 fe:ff:ff:ff:ff:           yes            0.00
2                 fe:ff:ff:fe:ff:           yes            0.00


# brctl showstp xenbr0

xenbr0 

bridge-id              8000.fefffffffff

designated-root        8000.fefffffffff

root-port              0                   path-cost             0

max-age                20.00               bridge-max-age        20.00

hello-time             2.00                bridge-hello-time     2.00

forward-delay          0.00                bridge-forward-delay  0.00

aging-time            300.01

hello-timer            1.43                tcn-timer             0.00

topology-change-timer  0.00                gc-timer              0.02

Other utilities which can be used to troubleshoot virtualization on Red Hat Enterprise Linux 5. All utilities mentioned can be found in the Server repositories of the Red Hat Enterprise Linux 5 Server distribution:

strace is a command which traces system calls and events received and used by another process.
vncviewer: connect to a VNC server running on your server or a virtual machine. Install vncviwer using the yum install vnc command.
vncserver: start a remote desktop on your server. Gives you the ability to run graphical user interfaces such as virt-manager via a remote session. Install vncserver using the yum install vnc-server command.