table of contents
TEXTDUMP(4) | Device Drivers Manual | TEXTDUMP(4) |
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 thedebug.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.
October 18, 2019 | Debian |