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Tools Available for Debugging & Analysis
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<small>''(Updated: Feb 2010)''</small>
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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.
  
There are several diagnostic tools available to debug Lustre; some are provided by the operating system, while others were developed and made available by the Lustre project.
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== Lustre Debugging Tools ==
  
Lustre tools -Components of same in-kernel debug mechanism
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The following in-kernel debug mechanisms are incorporated into the Lustre software:
  
    * debug logs: When a kernel module is first inserted, a circular debug buffer is allocated to hold substantial amount of debugging information (in megabytes or more). When the buffer fills up, it wraps around and discards the oldest information. We have added debug messages specifically for Lustre; they can be written out to this kernel log.
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* '''Debug logs.''' A circular debug buffer to which Lustre internal [[Lustre_Debugging_Procedures#Understanding_the_Lustre_debug_messaging_format|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 provides the facility for unlimited logging of the CDEBUG logs in Lustre.
 
    * /proc/sys/lnet/debug: Contains a mask that can be used to delimit the debugging information written out to the kernel debug logs.  
 
  
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* '''Debug daemon.''' The debug daemon controls logging of debug messages.
  
    * lctl: This tool is made available by Lustre. It is very useful to filter the kernel and extract useful information.
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* '''''/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.  
    * Lustre subsystem asserts: In case of asserts, a log will be written out to /tmp/lustre_log.<timestamp>.
 
    * lfs: A Lustre utility that can be used to get to a Lustre file's extended attributes (among other things).  
 
  
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For more information about using these tools to debug Lustre issues, see [[Lustre Debugging Procedures]].
  
    * leak_finder.pl: An extremely useful program that helps locate memory leaks in the code.
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These tools are also provided with the Lustre software:
  
External tools
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* '''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 [http://wiki.lustre.org/manual/LustreManual20_HTML/LustreDebugging.html#50438274_pgfId-1295889 Section 28.2.2: ''Using the lctl Tool to View Debug Messages''] and [http://wiki.lustre.org/manual/LustreManual20_HTML/SystemConfigurationUtilities_HTML.html#50438219_pgfId-1318224 Section 36.3: ''lctl''] in the [http://wiki.lustre.org/manual/LustreManual20_HTML/index.html ''Lustre Operations Manual''].
  
    * strace: Allows Lustre users to trace a system call.
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* '''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 [http://wiki.lustre.org/manual/LustreManual20_HTML/LustreTroubleshooting.html#50438198_pgfId-1291324 Section 26.1.2: ''Viewing Error Messages''] in the [http://wiki.lustre.org/manual/LustreManual20_HTML/index.html ''Lustre Operations Manual'']
    * /var/log/messages: The directory to which fatal or serious messages are printed by the syslogd.
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    * Crash dumps: On some kernels, a sysrq "c" is enabled which produces a crash dump. Lustre enhances this crash dump with a log dump (the last 64K of log) to the console.
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* '''lfs.''' This utility provides access to the extended attributes (EAs) of a Lustre file (along with other information). For more information about ''lfs'', see [http://wiki.lustre.org/manual/LustreManual20_HTML/UserUtilities_HTML.html#50438206_pgfId-1305210 Section 32.1: lfs] in the [http://wiki.lustre.org/manual/LustreManual20_HTML/index.html ''Lustre Operations Manual''].
    * debugfs: An nteractive Ext2 filesystem debugger.
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== External debugging tools ==
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====Tools for administrators and developers ====
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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.
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 +
* '''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.
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 +
* '''debugfs.''' Interactive file system debugger.
 +
 
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The following ''logging and data collection tools'' can be used to collect information for debugging Lustre kernel issues:
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* '''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 [http://kbase.redhat.com/faq/docs/DOC-6039 ''How do I configure kexec/kdump on Red Hat Enterprise Linux 5?'']. To download ''kdump'', go to the [http://fedoraproject.org/wiki/SystemConfig/kdump#Download Fedora Project Download] site.
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* '''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|Netconsole]].
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* '''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 [http://www.redhat.com/support/wpapers/redhat/netdump/ ''Red Hat, Inc.'s Network Console and Crash Dump Facility''].
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 +
==== 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 [http://www.sun.com/software/products/virtualbox/get.jsp?intcmp=2945 Get Sun Virtual Box].
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* '''VMware Server.''' Virtualization platform available as free introductory software at [http://downloads.vmware.com/d/info/datacenter_downloads/vmware_server/2_0 Download VMware Server].
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* '''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 [http://xen.org xen.org]
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A variety of ''debuggers and analysis tools'' are available including:
 +
 
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* '''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 [http://www.linuxtopia.org/online_books/redhat_linux_debugging_with_gdb/running.html ''Chapter 6. Running Programs Under gdb''] in the ''Red Hat Linux 4 Debugging with GDB'' guide.
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* '''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:
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 +
: - Red Hat Magazine article [http://magazine.redhat.com/2007/08/15/a-quick-overview-of-linux-kernel-crash-dump-analysis/ ''A quick overview of Linux kernel crash dump analysis''].
 +
: - [http://people.redhat.com/anderson/crash_whitepaper/#EXAMPLES Crash Usage: A Case Study] from the white paper ''Red Hat Crash Utility'' by David Anderson.
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: - Kernel Trap forum entry [http://kerneltrap.org/node/5758 Linux: Kernel Crash Dumps].
 +
: - White paper [http://www.google.com/url?sa=t&source=web&ct=res&cd=8&ved=0CCUQFjAH&url=http%3A%2F%2Fwww.kernel.sg%2Fpapers%2Fcrash-dump-analysis.pdf&rct=j&q=redhat+crash+dump&ei=6aQBS-ifK4T8tAPcjdiHCw&usg=AFQjCNEk03E3GDtAsawG3gfpwc1gGNELAg ''A Quick Overview of Linux Kernel Crash Dump Analysis''].

Latest revision as of 07:53, 20 January 2011

(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:

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:

  • 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.
  • 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.