TEXTDUMP(4)            FreeBSD Kernel Interfaces Manual            TEXTDUMP(4)

NAME
     textdump - textdump kernel dumping facility

SYNOPSIS
     options DDB
     options KDB

     options TEXTDUMP_PREFERRED
     options TEXTDUMP_VERBOSE

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 options INCLUDE_CONFIG_FILE 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.  One may also directly trigger
     a textdump in ddb(4) by running the command textdump dump.

     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).

     Additional kernel config(8) options:

     TEXTDUMP_PREFERRED  sets textdumps to be the default manner of doing
                         dumps.  This means there will be no need to sysctl(8)
                         or use the textdump set ddb(8) commands.

     TEXTDUMP_VERBOSE    will have the textdump facility be more verbose about
                         each file it is emitting as well as other diagnostics
                         useful to debug the textdump facility itself.

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 alllocks; textdump dump; 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.

FreeBSD 13.1-RELEASE-p6        October 18, 2019        FreeBSD 13.1-RELEASE-p6