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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
                  dbeug.ddb.textdump.do_panic sysctl.

     Kernel textdumps may be extracted using bsdtar(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

SEE ALSO

     bsdtar(1), ddb(4), tar(5), 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.