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_ddbsysctl. - config.txt
- Kernel configuration, if
options INCLUDE_CONFIG_FILEhas been compiled into the kernel. May be disabled by clearing thedebug.ddb.textdump.do_configsysctl. - 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_msgbufsysctl. - panic.txt
- Kernel panic string, if the kernel panicked before the dump was generated.
May be disabled by clearing the
debug.ddb.textdump.do_panicsysctl. - version.txt
- Kernel version string. My be disabled by clearing the
debug.ddb.textdump.do_versionsysctl.
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 setddb(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; 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.