Appendix A. Troubleshooting This chapter covers common problems and solutions for Red Hat Enterprise Linux 7 virtualization issues. Read this chapter to develop an understanding of some of the common problems associated with virtualization technologies. It is recommended that you experiment and test virtualization on Red Hat Enterprise Linux 7 to develop your troubleshooting skills. If you cannot find the answer in this document, there may be an answer online from the virtualization community. See Section D.1, "Online Resources" for a list of Linux virtualization websites. In addition, you will find further information on troubleshooting virtualization in RHEL 7 in the Red Hat Knowledgebase . A.1. Debugging and Troubleshooting Tools This section summarizes the system administrator applications, the networking utilities, and debugging tools. You can use these standard system administration tools and logs to assist with troubleshooting: kvm_stat - Retrieves KVM runtime statistics. For more information, see Section A.4, "kvm_stat" . ftrace - Traces kernel events. For more information, see the What is ftrace and how do I use it? solution article (subscription required) . vmstat - Displays virtual memory statistics. For more information, use the man vmstat command. iostat - Provides I/O load statistics. For more information, see the Red Hat Enterprise Linux Performance Tuning Guide lsof - Lists open files. For more information, use the man lsof command. systemtap - A scripting utility for monitoring the operating system. For more information, see the Red Hat Enterprise Linux Developer Guide . crash - Analyzes kernel crash dump data or a live system. For more information, see the Red Hat Enterprise Linux Kernel Crash Dump Guide . sysrq - A key combination that the kernel responds to even if the console is unresponsive. For more information, see the Red Hat Knowledge Base . These networking utilities can assist with troubleshooting virtualization networking problems: ip addr , ip route , and ip monitor tcpdump - diagnoses packet traffic on a network. This command is useful for finding network abnormalities and problems with network authentication. There is a graphical version of tcpdump , named wireshark . brctl - A networking utility that inspects and configures the Ethernet bridge configuration in the Linux kernel. For example: Listed below are some other useful commands for troubleshooting virtualization: strace is a command which traces system calls and events received and used by another process. vncviewer connects to a VNC server running on your server or a virtual machine. Install vncviewer using the yum install tigervnc command. vncserver starts a remote desktop on your server. Gives you the ability to run graphical user interfaces, such as virt-manager, using a remote session. Install vncserver using the yum install tigervnc-server command. In addition to all the commands listed above, examining virtualization logs can be helpful. For more information, see Section A.6, "Virtualization Logs" .

Commands:
brctl show bridge-name bridge-id STP enabled interfaces ----------------------------------------------------------------------------- virtbr0 8000.feffffff yes eth0 brctl showmacs virtbr0 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 virtbr0 virtbr0 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