NAME¶
textdump —
textdump kernel dumping
facility
SYNOPSIS¶
options KDB
options DDB
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 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.
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).
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 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
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.