Diagnostic and Debugging Tools

(Updated: Feb 2010)

A variety of diagnostic and analysis tools are available to debug issues with the Lustre™ software. Some of these are provided in Linux distributions, while others have been developed and are made available by the Lustre project.

Lustre Debugging Tools

The following in-kernel debug mechanisms are incorporated into the Lustre software:

• Debug logs. A circular debug buffer to which Lustre internal debug messages are written (in contrast to error messages, which are printed to the syslog or console). Entries to the Lustre debug log are controlled by the mask set by /proc/sys/lnet/debug. The log size defaults to 5 MB per CPU but can be increased as a busy system will quickly overwrite 5 MB. When the buffer fills, the oldest information is discarded.

• Debug daemon. The debug daemon controls logging of debug messages.

• /proc/sys/lnet/debug. This file contains a mask that can be used to delimit the debugging information written out to the kernel debug logs.

For more information about using these tools to debug Lustre issues, see Lustre Debugging Procedures.

These tools are also provided with the Lustre software:

• lctl. This tool is used with the debug_kernel option to manually dump the Lustre debugging log or post-process debugging logs that are dumped automatically. For more information about the lctl tool, see Section 28.2.2: Using the lctl Tool to View Debug Messages and Section 36.3: lctl in the Lustre Operations Manual.

• Lustre subsystem asserts. A panic-style assertion (LBUG) in the kernel causes Lustre to dump the debug log to the file /tmp/lustre-log.<timestamp> where it can be retrieved after a reboot. For more information, see Section 26.1.2: Viewing Error Messages in the Lustre Operations Manual

• lfs. This utility provides access to the extended attributes (EAs) of a Lustre file (along with other information). For more information about lfs, see Section 32.1: lfs in the Lustre Operations Manual.

External debugging tools

Tools for administrators and developers

The tools described in this section are provided in the Linux kernel or are available at an external website. For information about using some of these tools for Lustre debugging, see Lustre Debugging Procedures and Lustre Debugging for Developers.

Some general debugging tools provided as a part of the standard Linux distro are:

• strace. This tool allows a system call to be traced.

• /var/log/messages. syslogd prints fatal or serious messages at this log.

• Crash dumps. On crash-dump enabled kernels, sysrq c produces a crash dump. Lustre enhances this crash dump with a log dump (the last 64 KB of the log) to the console.

• debugfs. Interactive file system debugger.

The following logging and data collection tools can be used to collect information for debugging Lustre kernel issues:

• kdump. A Linux kernel crash utility useful for debugging a system running Red Hat Enterprise Linux. For more information about kdump, see the Red Hat knowledge base article How do I configure kexec/kdump on Red Hat Enterprise Linux 5?. To download kdump, go to the Fedora Project Download site.

• netconsole. Supports kernel-level network logging over UDP. A system requires (SysRq) allows users to collect relevant data through netconsole. For more information, see Netconsole.

• netdump. A crash dump utility from Red Hat that allows memory images to be dumped over a network to a central server for analysis. The netdump utility was replaced by kdump in RHEL 5. For more information about netdump, see Red Hat, Inc.'s Network Console and Crash Dump Facility.

Tools for developers

The tools described in this section may be useful for debugging Lustre™ in a development environment.

Of general interest is:

• leak_finder.pl. This program provided with Lustre is useful for finding memory leaks in the code.

A virtual machine is often used to create an isolated development and test environment. Some commonly-used virtual machines are:

• VirtualBox Open Source Edition. Provides enterprise-class virtualization capability for all major platforms and is available free from Sun Microsystems at Get Sun Virtual Box.

• VMware Server. Virtualization platform available as free introductory software at Download VMware Server.

• Xen. A para-virtualized environment with virtualization capabilities similar to VMware Server and Virtual Box. However, Xen allows the use of modified kernels to provide near-native performance and the ability to emulate shared storage. For more information, see Using Xen with Lustre or go to xen.org

A variety of debuggers and analysis tools are available including:

• kgdb. The Linux Kernel Source Level Debugger kgdb is used in conjunction with the GNU Debugger gdb for debugging the Linux kernel. For more information about using kgdb with gdb, see Chapter 6. Running Programs Under gdb in the Red Hat Linux 4 Debugging with GDB guide.

• crash. Used to analyze saved crash dump data when a system had panicked or locked up or appears unresponsive. For more information about using crash to analyze a crash dump, see:

- Red Hat Magazine article A quick overview of Linux kernel crash dump analysis.

- Crash Usage: A Case Study from the white paper Red Hat Crash Utility by David Anderson.

- Kernel Trap forum entry Linux: Kernel Crash Dumps.

- White paper A Quick Overview of Linux Kernel Crash Dump Analysis.