dumpon(8) [freebsd man page]
DUMPON(8) BSD System Manager's Manual DUMPON(8) NAME
dumpon -- specify a device for crash dumps SYNOPSIS
dumpon [-v] special_file dumpon [-v] off dumpon [-v] -l DESCRIPTION
The dumpon utility is used to specify a device where the kernel can save a crash dump in the case of a panic. Calls to dumpon normally occur from the system multi-user initialization file /etc/rc, controlled by the ``dumpdev'' variable in the boot time configuration file /etc/rc.conf. The default type of kernel crash dump is the mini crash dump. Mini crash dumps hold only memory pages in use by the kernel. Alternatively, full memory dumps can be enabled by setting the debug.minidump sysctl(8) variable to 0. For systems using full memory dumps, the size of the specified dump device must be at least the size of physical memory. Even though an additional 64 kB header is added to the dump, the BIOS for a platform typically holds back some memory, so it is not usually necessary to size the dump device larger than the actual amount of RAM available in the machine. Also, when using full memory dumps, the dumpon utility will refuse to enable a dump device which is smaller than the total amount of physical memory as reported by the hw.physmem sysctl(8) vari- able. The -l flag causes dumpon to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is configured. The -v flag causes dumpon to be verbose about its activity. IMPLEMENTATION NOTES
Since a panic(9) condition may occur in a situation where the kernel cannot trust its internal representation of the state of any given file system, one of the system swap devices, and not a device containing a file system, should be used as the dump device. The dumpon utility operates by opening special_file and making a DIOCSKERNELDUMP ioctl(2) request on it to save kernel crash dumps. If special_file is the text string: ``off'', dumpon performs a DIOCSKERNELDUMP ioctl(2) on /dev/null and thus instructs the kernel not to save crash dumps. Since dumpon cannot be used during kernel initialization, the dumpdev variable of loader(8) must be used to enable dumps for system panics which occur during kernel initialization. FILES
/dev/{ada,da}?s?b standard swap areas /etc/rc.conf boot-time system configuration SEE ALSO
fstab(5), rc.conf(5), config(8), init(8), loader(8), rc(8), savecore(8), swapon(8), panic(9) HISTORY
The dumpon utility appeared in FreeBSD 2.1. BUGS
Because the file system layer is already dead by the time a crash dump is taken, it is not possible to send crash dumps directly to a file. BSD
October 8, 2014 BSD
Check Out this Related Man Page
TEXTDUMP(4) BSD Kernel Interfaces Manual TEXTDUMP(4) 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. 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 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 cap- ture, 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. BSD
December 24, 2008 BSD