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NAME

     textdump — textdump kernel dumping facility

SYNOPSIS

     options KDB
     options DDB

DESCRIPTION

     The textdump facility allows the capture of kernel debugging information to disk in a human-
     readable rather than the machine-readable form normally used with kernel memory dumps and
     minidumps.  This representation, while less complete in that it does not capture full kernel
     state, can provide debugging information in a more compact, portable, and persistent form
     than a traditional dump.  By combining textdump with other ddb(4) facilities, such as
     scripting and output capture, detailed bug information can be captured in a fully automated
     manner.

FORMAT

     textdump data is stored in a dump partition in the same style as a regular memory dump, and
     will be automatically extracted by savecore(8) if present on boot.

     textdump files are stored in the tar(5) format, and consist of one or more text files, each
     storing a particular type of debugging output.  The following parts may be present:

     ddb.txt      Captured ddb(4) output, if the capture facility has been used.  May be disabled
                  by clearing the debug.ddb.textdump.do_ddb sysctl.

     config.txt   Kernel configuration, if has been compiled into the kernel.  May be disabled by
                  clearing the debug.ddb.textdump.do_config sysctl.

     msgbuf.txt   Kernel message buffer, including recent console output if the capture facility
                  has been used.  May be disabled by clearing the debug.ddb.textdump.do_msgbuf
                  sysctl.

     panic.txt    Kernel panic string, if the kernel panicked before the dump was generated.  May
                  be disabled by clearing the debug.ddb.textdump.do_panic sysctl.

     version.txt  Kernel version string.  My be disabled by clearing the
                  debug.ddb.textdump.do_version sysctl.

     Kernel textdumps may be extracted using tar(1).

CONFIGURATION

     The textdump facility is enabled as part of the kernel debugger using options KDB and
     options DDB.  By default, kernel dumps generated on panic or via explicit requests for a
     dump will be regular memory dumps; however, by using the textdump set command in ddb(4), or
     by setting the debug.ddb.textdump.pending sysctl to 1 using sysctl(8), it is possible to
     request that the next dump be a textdump.

     If at the ddb(4) command line, the commands textdump set, textdump status, and textdump
     unset may be used to set, query, and clear the textdump pending flag.

     As with regular kernel dumps, a dump partition must be automatically or manually configured
     using dumpon(8).

EXAMPLES

     In the following example, the script kdb.enter.panic will run when the kernel debugger is
     entered as a result of a panic, enable output capture, dump several useful pieces of
     debugging information, and then invoke panic in order to force a kernel dump to be written
     out followed by a reboot:

           script kdb.enter.panic=textdump set; capture on; show allpcpu; bt;
             ps; alltrace; show alllock; call doadump; reset

     In the following example, the script kdb.enter.witness will run when the kernel debugger is
     entered as a result of a witness violation, printing lock-related information for the user:

           script kdb.enter.witness=show locks

     These scripts may also be configured using the ddb(8) utility.

SEE ALSO

     tar(1), ddb(4), tar(5), ddb(8), dumpon(8), savecore(8), sysctl(8)

HISTORY

     The textdump facility first appeared in FreeBSD 7.1.

AUTHORS

     The textdump facility was created by Robert N. M. Watson.