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Diagnostic and Debugging Tools

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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.

These tools are also provided with the Lustre software:

  • Lustre subsystem asserts. A panic-style assertion 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. Cliff review.

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.

Some general debugging tools are: Do we need to provide links to more info for these?

  • 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:

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 is useful for finding memory leaks in the code.

A virtual machine is often used to create an isolated development and test environment. Some popular 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.
  • 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]
Parinay is planning to "include KVM here and how lustre can be deployed on it". See BZ 21381

A variety of debuggers and analysis tools are available including:

  • kgdb. A source-level kernel debugger that allows remote debugging using conman. kgdb provides a special set of hooks for a Linux kernel to attach gdb from another machine over a serial console. We provide kgdb patches for some kernels like rhel4 with the Lustre patches (these are not patched in by default). Update needed?

For more information, see KGDB and Using kgdb with UDP.

Also see Chapter 6. Running Programs Under gdb in the Red Hat Linux 4 Debugging with GDB guide.

NOTES - KGDB topic - ask Alex BZZZ or Robert Reid - instructions are old and not specific to Lustre - do we want to keep these around or find link to eternal site - sourceforge site has a ton of information.

1. Get patches from ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.5/

- VmWare instructions on this page are specific to using cdb with VmWare - but are OLD!

- For other external tools - provide pointer rather than maintain documentation on wiki. See IX4

  • lcrash. A utility that generates detailed kernel information and provides the ability to generate reports about system crash dumps. For more information, see man page. Is this a good link?
  • crash. Red Hat Crash Utility?? is used to analyze saved crash dump data when a system had panicked or locked up or appears unresponsive.


crash vmlinux crash_dump keep this?
For more information about using crash to analyze crash dump output, 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.

NOTES See Tien's suggestion BZ 21334 [[1]]