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.

Debian                                          October 18, 2019                                     TEXTDUMP(4)