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textdump — textdump kernel dumping facility
options KDB options DDB
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).
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 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.
The textdump facility first appeared in FreeBSD 7.1.
The textdump facility was created by Robert N. M. Watson.