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.
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; 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.