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textdump - textdump kernel dumping facility
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
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
config.txt Kernel configuration, if has been compiled into the kernel.
May be disabled by clearing the debug.ddb.textdump.do_config
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
version.txt Kernel version string. My be disabled by clearing the
Kernel textdumps may be extracted using bsdtar(1).
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).
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
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
bsdtar(1), ddb(4), tar(5), dumpon(8), savecore(8), sysctl(8)
The textdump facility first appeared in FreeBSD 7.1.
The textdump facility was created by Robert N. M. Watson.