2 .\" Mach Operating System
3 .\" Copyright (c) 1991,1990 Carnegie Mellon University
4 .\" Copyright (c) 2007 Robert N. M. Watson
5 .\" All Rights Reserved.
7 .\" Permission to use, copy, modify and distribute this software and its
8 .\" documentation is hereby granted, provided that both the copyright
9 .\" notice and this permission notice appear in all copies of the
10 .\" software, derivative works or modified versions, and any portions
11 .\" thereof, and that both notices appear in supporting documentation.
13 .\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
14 .\" CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
15 .\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
17 .\" Carnegie Mellon requests users of this software to return to
19 .\" Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
20 .\" School of Computer Science
21 .\" Carnegie Mellon University
22 .\" Pittsburgh PA 15213-3890
24 .\" any improvements or extensions that they make and grant Carnegie Mellon
25 .\" the rights to redistribute these changes.
27 .\" changed a \# to #, since groff choked on it.
31 .\" Revision 1.1 1993/07/15 18:41:02 brezak
34 .\" Revision 2.6 92/04/08 08:52:57 rpd
36 .\" [92/01/17 14:19:22 jsb]
37 .\" Changes for OSF debugger modifications.
40 .\" Revision 2.5 91/06/25 13:50:22 rpd
41 .\" Added some watchpoint explanation.
44 .\" Revision 2.4 91/06/17 15:47:31 jsb
45 .\" Added documentation for continue/c, match, search, and watchpoints.
46 .\" I've not actually explained what a watchpoint is; maybe Rich can
47 .\" do that (hint, hint).
48 .\" [91/06/17 10:58:08 jsb]
50 .\" Revision 2.3 91/05/14 17:04:23 mrt
51 .\" Correcting copyright
53 .\" Revision 2.2 91/02/14 14:10:06 mrt
54 .\" Changed to new Mach copyright
55 .\" [91/02/12 18:10:12 mrt]
57 .\" Revision 2.2 90/08/30 14:23:15 dbg
68 .Nd interactive kernel debugger
70 In order to enable kernel debugging facilities include:
71 .Bd -ragged -offset indent
76 To prevent activation of the debugger on kernel
78 .Bd -ragged -offset indent
79 .Cd options KDB_UNATTENDED
82 In order to print a stack trace of the current thread on the console
84 .Bd -ragged -offset indent
88 To print the numerical value of symbols in addition to the symbolic
89 representation, define:
90 .Bd -ragged -offset indent
91 .Cd options DDB_NUMSYM
96 backend, so that remote debugging with
99 .Bd -ragged -offset indent
105 kernel debugger is an interactive debugger with a syntax inspired by
107 If linked into the running kernel,
108 it can be invoked locally with the
112 The debugger is also invoked on kernel
115 .Va debug.debugger_on_panic
117 MIB variable is set non-zero,
123 The current location is called
128 a hexadecimal format at a prompt.
135 to the address of the last line
136 examined or the last location modified, and set
139 the next location to be examined or changed.
140 Other commands do not change
147 The general command syntax is:
148 .Ar command Ns Op Li / Ns Ar modifier
149 .Ar address Ns Op Li , Ns Ar count
151 A blank line repeats the previous command from the address
154 count 1 and no modifiers.
167 to be 1 for printing commands or infinity for stack traces.
171 debugger has a pager feature (like the
175 If an output line exceeds the number set in the
177 variable, it displays
179 and waits for a response.
180 The valid responses for it are:
182 .Bl -tag -compact -width ".Li SPC"
188 abort the current command, and return to the command input mode
193 provides a small (currently 10 items) command history, and offers
196 command line editing capabilities.
200 control keys, the usual
202 arrow keys may be used to
203 browse through the history buffer, and move the cursor within the
206 .Bl -tag -width indent -compact
209 Display the addressed locations according to the formats in the modifier.
210 Multiple modifier formats display multiple locations.
211 If no format is specified, the last format specified for this command
214 The format characters are:
215 .Bl -tag -compact -width indent
217 look at by bytes (8 bits)
219 look at by half words (16 bits)
221 look at by long words (32 bits)
223 print the location being displayed
225 print the location with a line number if possible
227 display in unsigned hex
229 display in signed hex
231 display in unsigned octal
233 display in signed decimal
235 display in unsigned decimal
237 display in current radix, signed
239 display low 8 bits as a character.
240 Non-printing characters are displayed as an octal escape code (e.g.,
243 display the null-terminated string at the location.
244 Non-printing characters are displayed as octal escapes.
246 display in unsigned hex with character dump at the end of each line.
247 The location is also displayed in hex at the beginning of each line.
249 display as an instruction
251 display as an instruction with possible alternate formats depending on the
253 .Bl -tag -width ".Tn powerpc" -compact
266 display a symbol name for the pointer stored at the address
273 command with the last specified parameters to it
274 except that the next address displayed by it is used as the start address.
280 command with the last specified parameters to it
281 except that the last start address subtracted by the size displayed by it
282 is used as the start address.
284 .It Ic print Ns Op Li / Ns Cm acdoruxz
285 .It Ic p Ns Op Li / Ns Cm acdoruxz
288 according to the modifier character (as described above for
291 .Cm a , x , z , o , d , u , r ,
294 If no modifier is specified, the last one specified to it is used.
297 can be a string, in which case it is printed as it is.
299 .Bd -literal -offset indent
300 print/x "eax = " $eax "\enecx = " $ecx "\en"
304 .Bd -literal -offset indent
310 .Ic write Ns Op Li / Ns Cm bhl
311 .Ar addr expr1 Op Ar expr2 ...
314 .Ic w Ns Op Li / Ns Cm bhl
315 .Ar addr expr1 Op Ar expr2 ...
317 Write the expressions specified after
319 on the command line at succeeding locations starting with
321 The write unit size can be specified in the modifier with a letter
327 (long word) respectively.
329 long word is assumed.
332 since there is no delimiter between expressions, strange
334 It is best to enclose each expression in parentheses.
336 .It Ic set Li $ Ns Ar variable Oo Li = Oc Ar expr
337 Set the named variable or register with the value of
339 Valid variable names are described below.
341 .It Ic break Ns Op Li / Ns Cm u
342 .It Ic b Ns Op Li / Ns Cm u
347 is supplied, continues
349 \- 1 times before stopping at the
351 If the break point is set, a break point number is
354 This number can be used in deleting the break point
355 or adding conditions to it.
359 modifier is specified, this command sets a break point in user
363 option, the address is considered to be in the kernel
364 space, and a wrong space address is rejected with an error message.
365 This modifier can be used only if it is supported by machine dependent
369 If a user text is shadowed by a normal user space debugger,
370 user space break points may not work correctly.
372 point at the low-level code paths may also cause strange behavior.
374 .It Ic delete Ar addr
376 .It Ic delete Li # Ns Ar number
377 .It Ic d Li # Ns Ar number
378 Delete the break point.
379 The target break point can be specified by a
380 break point number with
384 specified in the original
388 .It Ic watch Ar addr Ns Li , Ns Ar size
389 Set a watchpoint for a region.
390 Execution stops when an attempt to modify the region occurs.
393 argument defaults to 4.
394 If you specify a wrong space address, the request is rejected
395 with an error message.
398 Attempts to watch wired kernel memory
399 may cause unrecoverable error in some systems such as i386.
400 Watchpoints on user addresses work best.
402 .It Ic hwatch Ar addr Ns Li , Ns Ar size
403 Set a hardware watchpoint for a region if supported by the
405 Execution stops when an attempt to modify the region occurs.
408 argument defaults to 4.
411 The hardware debug facilities do not have a concept of separate
412 address spaces like the watch command does.
415 for setting watchpoints on kernel address locations only, and avoid
416 its use on user mode address spaces.
418 .It Ic dhwatch Ar addr Ns Li , Ns Ar size
419 Delete specified hardware watchpoint.
421 .It Ic step Ns Op Li / Ns Cm p
422 .It Ic s Ns Op Li / Ns Cm p
425 times (the comma is a mandatory part of the syntax).
428 modifier is specified, print each instruction at each step.
429 Otherwise, only print the last instruction.
432 depending on machine type, it may not be possible to
433 single-step through some low-level code paths or user space code.
434 On machines with software-emulated single-stepping (e.g., pmax),
435 stepping through code executed by interrupt handlers will probably
438 .It Ic continue Ns Op Li / Ns Cm c
439 .It Ic c Ns Op Li / Ns Cm c
440 Continue execution until a breakpoint or watchpoint.
443 modifier is specified, count instructions while executing.
444 Some machines (e.g., pmax) also count loads and stores.
447 when counting, the debugger is really silently single-stepping.
448 This means that single-stepping on low-level code may cause strange
451 .It Ic until Ns Op Li / Ns Cm p
452 Stop at the next call or return instruction.
455 modifier is specified, print the call nesting depth and the
456 cumulative instruction count at each call or return.
458 only print when the matching return is hit.
460 .It Ic next Ns Op Li / Ns Cm p
461 .It Ic match Ns Op Li / Ns Cm p
462 Stop at the matching return instruction.
465 modifier is specified, print the call nesting depth and the
466 cumulative instruction count at each call or return.
467 Otherwise, only print when the matching return is hit.
470 .Ic trace Ns Op Li / Ns Cm u
475 .Ic t Ns Op Li / Ns Cm u
480 .Ic where Ns Op Li / Ns Cm u
485 .Ic bt Ns Op Li / Ns Cm u
492 option traces user space; if omitted,
496 The optional argument
498 is the number of frames to be traced.
501 is omitted, all frames are printed.
504 User space stack trace is valid
505 only if the machine dependent code supports it.
508 .Ic search Ns Op Li / Ns Cm bhl
516 This command might fail in interesting
517 ways if it does not find the searched-for value.
520 does not always recover from touching bad memory.
523 argument limits the search.
526 .It Ic show Cm all procs Ns Op Li / Ns Cm m
527 .It Ic ps Ns Op Li / Ns Cm m
528 Display all process information.
529 The process information may not be shown if it is not
530 supported in the machine, or the bottom of the stack of the
531 target process is not in the main memory at that time.
534 modifier will alter the display to show VM map
535 addresses for the process and not show other information.
538 .It Ic show Cm all ttys
539 Show all TTY's within the system.
542 but also includes the address of the TTY structure.
545 .It Ic show Cm allchains
546 Show the same information like "show lockchain" does, but
547 for every thread in the system.
550 .It Ic show Cm alllocks
551 Show all locks that are currently held.
552 This command is only available if
554 is included in the kernel.
557 .It Ic show Cm allpcpu
558 The same as "show pcpu", but for every CPU present in the system.
561 .It Ic show Cm allrman
562 Show information related with resource management, including
563 interrupt request lines, DMA request lines, I/O ports and I/O memory
568 Dump data about APIC IDT vector mappings.
571 .It Ic show Cm breaks
572 Show breakpoints set with the "break" command.
575 .It Ic show Cm buffer
576 Show buffer structure of
579 Such a structure is used within the
581 kernel for the I/O subsystem
583 For an exact interpretation of the output, please see the
588 .It Ic show Cm cbstat
589 Show brief information about the TTY subsystem.
592 .It Ic show Cm conifhk
593 Lists hooks currently waiting for completion in
594 run_interrupt_driven_config_hooks().
597 .It Ic show Cm cpusets
598 Print numbered root and assigned CPU affinity sets.
604 .It Ic show Cm cyrixreg
605 Show registers specific to the Cyrix processor.
608 .It Ic show Cm domain Ar addr
609 Print protocol domain structure
615 header file for more details on the exact meaning of the structure fields.
618 .It Ic show Cm ffs Op Ar addr
619 Show brief information about ffs mount at the address
621 if argument is given.
622 Otherwise, provides the summary about each ffs mount.
625 .It Ic show Cm file Ar addr
626 Show information about the file structure
633 Show information about every file structure in the system.
636 .It Ic show Cm freepages
637 Show the number of physical pages in each of the free lists.
640 .It Ic show Cm geom Op Ar addr
643 argument is not given, displays the entire GEOM topology.
646 is given, displays details about the given GEOM object (class, geom,
647 provider or consumer).
652 The first column specifies the IDT vector.
653 The second one is the name of the interrupt/trap handler.
654 Those functions are machine dependent.
657 .It Ic show Cm inodedeps Op Ar addr
658 Show brief information about each inodedep structure.
661 is given, only inodedeps belonging to the fs located at the
662 supplied address are shown.
665 .It Ic show Cm inpcb Ar addr
666 Show information on IP Control Block
673 Dump information about interrupt handlers.
676 .It Ic show Cm intrcnt
677 Dump the interrupt statistics.
681 Show interrupt lines and their respective kernel threads.
690 shows, also list kernel internal details.
694 Show information from the local APIC registers for this CPU.
697 .It Ic show Cm lock Ar addr
699 The output format is as follows:
700 .Bl -tag -offset 0 -width "flags"
703 Possible types include
711 Flags passed to the lock initialization function.
712 For exact possibilities see manual pages of possible lock types.
714 Current state of a lock.
723 .It Ic show Cm lockchain Ar addr
724 Show all threads a particular thread at address
726 is waiting on based on non-sleepable and non-spin locks.
729 .It Ic show Cm lockedbufs
730 Show the same information as "show buf", but for every locked
735 .It Ic show Cm lockedvnods
736 List all locked vnodes in the system.
740 Prints all locks that are currently acquired.
741 This command is only available if
743 is included in the kernel.
746 .It Ic show Cm locktree
749 .It Ic show Cm malloc
752 memory allocator statistics.
753 The output format is as follows:
755 .Bl -tag -compact -offset indent -width "Requests"
757 Specifies a type of memory.
758 It is the same as a description string used while defining the
759 given memory type with
760 .Xr MALLOC_DECLARE 9 .
762 Number of memory allocations of the given type, for which
764 has not been called yet.
766 Total memory consumed by the given allocation type.
768 Number of memory allocation requests for the given
772 The same information can be gathered in userspace with
776 .It Ic show Cm map Ns Oo Li / Ns Cm f Oc Ar addr
781 modifier is specified the
782 complete map is printed.
785 .It Ic show Cm msgbuf
786 Print the system's message buffer.
787 It is the same output as in the
790 It is useful if you got a kernel panic, attached a serial cable
791 to the machine and want to get the boot messages from before the
795 Displays short info about all currently mounted file systems.
797 .It Ic show Cm mount Ar addr
798 Displays details about the given mount point.
802 .It Ic show Cm object Ns Oo Li / Ns Cm f Oc Ar addr
803 Prints the VM object at
807 option is specified the
808 complete object is printed.
812 Show statistics on VM pages.
816 Show statistics on VM page queues.
819 .It Ic show Cm pciregs
820 Print PCI bus registers.
821 The same information can be gathered in userspace by running
822 .Dq Nm pciconf Fl lv .
826 Print current processor state.
827 The output format is as follows:
829 .Bl -tag -compact -offset indent -width "spin locks held:"
831 Processor identifier.
833 Thread pointer, process identifier and the name of the process.
835 Control block pointer.
841 CPU identifier coming from APIC.
844 .It Ic spin locks held
845 Names of spin locks held.
849 .It Ic show Cm pgrpdump
850 Dump process groups present within the system.
853 .It Ic show Cm proc Op Ar addr
856 is specified, print information about the current process.
857 Otherwise, show information about the process at address
861 .It Ic show Cm procvm
862 Show process virtual memory layout.
865 .It Ic show Cm protosw Ar addr
866 Print protocol switch structure
872 .It Ic show Cm registers Ns Op Li / Ns Cm u
873 Display the register set.
876 modifier is specified, it displays user registers instead of
877 kernel registers or the currently saved one.
882 modifier depends on the machine.
883 If not supported, incorrect information will be displayed.
886 .It Ic show Cm rman Ar addr
887 Show resource manager object
891 Addresses of particular pointers can be gathered with "show allrman"
896 Show real time clock value.
897 Useful for long debugging sessions.
900 .It Ic show Cm sleepchain
901 Show all the threads a particular thread is waiting on based on
905 .It Ic show Cm sleepq
906 .It Ic show Cm sleepqueue
907 Both commands provide the same functionality.
909 .Vt struct sleepqueue
911 Sleepqueues are used within the
913 kernel to implement sleepable
914 synchronization primitives (thread holding a lock might sleep or
915 be context switched), which at the time of writing are:
923 .It Ic show Cm sockbuf Ar addr
924 .It Ic show Cm socket Ar addr
931 Output consists of all values present in structures mentioned.
932 For exact interpretation and more details, visit
937 .It Ic show Cm sysregs
938 Show system registers (e.g.,
941 Not present on some platforms.
944 .It Ic show Cm tcpcb Ar addr
945 Print TCP control block
949 For exact interpretation of output, visit
954 .It Ic show Cm thread Op Ar addr
957 is specified, show detailed information about current thread.
958 Otherwise, information about thread at
963 .It Ic show Cm threads
964 Show all threads within the system.
965 Output format is as follows:
967 .Bl -tag -width "PPID" -compact -offset indent -width "Second column"
969 Thread identifier (TID)
971 Thread structure address
977 .It Ic show Cm tty Ar addr
978 Display the contents of a TTY structure in a readable form.
981 .It Ic show Cm turnstile Ar addr
986 Turnstiles are structures used within the
989 synchronization primitives which, while holding a specific type of lock, cannot
990 sleep or context switch to another thread.
991 Currently, those are:
998 Show UMA allocator statistics.
999 Output consists five columns:
1001 .Bl -tag -compact -offset indent -width "Requests"
1003 Name of the UMA zone.
1004 The same string that was passed to
1006 as a first argument.
1008 Size of a given memory object (slab).
1010 Number of slabs being currently used.
1012 Number of free slabs within the UMA zone.
1014 Number of allocations requests to the given zone.
1017 The very same information might be gathered in the userspace
1022 .It Ic show Cm unpcb Ar addr
1023 Shows UNIX domain socket private control block
1025 present at the address
1029 .It Ic show Cm vmochk
1030 Prints, whether the internal VM objects are in a map somewhere
1031 and none have zero ref counts.
1034 .It Ic show Cm vmopag
1035 This is supposed to show physical addresses consumed by a
1037 Currently, it is not possible to use this command when
1039 is compiled in the kernel.
1042 .It Ic show Cm vnode Op Ar addr
1047 For the exact interpretation of the output, look at the
1052 .It Ic show Cm vnodebufs Ar addr
1053 Shows clean/dirty buffer lists of the vnode located at
1057 .It Ic show Cm watches
1058 Displays all watchpoints.
1059 Shows watchpoints set with "watch" command.
1062 .It Ic show Cm witness
1063 Shows information about lock acquisition coming from the
1069 Toggles between remote GDB and DDB mode.
1070 In remote GDB mode, another machine is required that runs
1072 using the remote debug feature, with a connection to the serial
1073 console port on the target machine.
1074 Currently only available on the
1081 .It Ic kill Ar sig pid
1086 The signal is acted on upon returning from the debugger.
1087 This command can be used to kill a process causing resource contention
1088 in the case of a hung system.
1091 for a list of signals.
1092 Note that the arguments are reversed relative to
1095 .It Ic reboot Op Ar seconds
1096 .It Ic reset Op Ar seconds
1097 Hard reset the system.
1098 If the optional argument
1100 is given, the debugger will wait for this long, at most a week,
1104 Print a short summary of the available commands and command
1109 .It Ic capture reset
1110 .It Ic capture status
1112 supports a basic output capture facility, which can be used to retrieve the
1113 results of debugging commands from userpsace using
1116 enables output capture;
1120 will clear the capture buffer and disable capture.
1122 will report current buffer use, buffer size, and disposition of output
1125 Userspace processes may inspect and manage
1130 .Dv debug.ddb.capture.bufsize
1131 may be used to query or set the current capture buffer size.
1133 .Dv debug.ddb.capture.maxbufsize
1134 may be used to query the compile-time limit on the capture buffer size.
1136 .Dv debug.ddb.capture.bytes
1137 may be used to query the number of bytes of output currently in the capture
1140 .Dv debug.ddb.capture.data
1141 returns the contents of the buffer as a string to an appropriately privileged
1144 This facility is particularly useful in concert with the scripting and
1146 facilities, allowing scripted debugging output to be captured and
1147 committed to disk as part of a textdump for later analysis.
1148 The contents of the capture buffer may also be inspected in a kernel core dump
1156 Run, define, list, and delete scripts.
1159 section for more information on the scripting facility.
1162 .It Ic textdump status
1163 .It Ic textdump unset
1166 command may be used to force the next kernel core dump to be a textdump
1167 rather than a traditional memory dump or minidump.
1169 reports whether a textdump has been scheduled.
1171 cancels a request to perform a textdump as the next kernel core dump.
1172 More information may be found in
1176 The debugger accesses registers and variables as
1178 Register names are as in the
1179 .Dq Ic show Cm registers
1181 Some variables are suffixed with numbers, and may have some modifier
1182 following a colon immediately after the variable name.
1183 For example, register variables can have a
1185 modifier to indicate user register (e.g.,
1188 Built-in variables currently supported are:
1190 .Bl -tag -width ".Va tabstops" -compact
1192 Input and output radix.
1194 Addresses are printed as
1195 .Dq Ar symbol Ns Li + Ns Ar offset
1201 The width of the displayed line.
1203 The number of lines.
1204 It is used by the built-in pager.
1207 .It Va work Ns Ar xx
1210 can take values from 0 to 31.
1213 Most expression operators in C are supported except
1221 .Bl -tag -width ".No Identifiers"
1223 The name of a symbol is translated to the value of the symbol, which
1224 is the address of the corresponding object.
1228 can be used in the identifier.
1229 If supported by an object format dependent routine,
1231 .Oo Ar filename : Oc Ar func : lineno ,
1233 .Oo Ar filename : Oc Ns Ar variable ,
1235 .Oo Ar filename : Oc Ns Ar lineno
1236 can be accepted as a symbol.
1238 Radix is determined by the first two letters:
1244 decimal; otherwise, follow current radix.
1250 address of the start of the last line examined.
1255 this is only changed by
1261 last address explicitly specified.
1262 .It Li $ Ns Ar variable
1263 Translated to the value of the specified variable.
1264 It may be followed by a
1266 and modifiers as described above.
1267 .It Ar a Ns Li # Ns Ar b
1268 A binary operator which rounds up the left hand side to the next
1269 multiple of right hand side.
1272 It may be followed by a
1274 and modifiers as described above.
1278 supports a basic scripting facility to allow automating tasks or responses to
1280 Each script consists of a list of DDB commands to be executed sequentially,
1281 and is assigned a unique name.
1282 Certain script names have special meaning, and will be automatically run on
1285 events if scripts by those names have been defined.
1289 command may be used to define a script by name.
1290 Scripts consist of a series of
1292 commands separated with the
1296 .Bd -literal -offset indent
1297 script kdb.enter.panic=bt; show pcpu
1298 script lockinfo=show alllocks; show lockedvnods
1303 command lists currently defined scripts.
1307 command execute a script by name.
1309 .Bd -literal -offset indent
1315 command may be used to delete a script by name.
1317 .Bd -literal -offset indent
1318 unscript kdb.enter.panic
1321 These functions may also be performed from userspace using the
1325 Certain scripts are run automatically, if defined, for specific
1328 The follow scripts are run when various events occur:
1329 .Bl -tag -width kdb.enter.powerfail
1330 .It Dv kdb.enter.acpi
1331 The kernel debugger was entered as a result of an
1334 .It Dv kdb.enter.bootflags
1335 The kernel debugger was entered at boot as a result of the debugger boot
1337 .It Dv kdb.enter.break
1338 The kernel debugger was entered as a result of a serial or console break.
1339 .It Dv kdb.enter.cam
1340 The kernel debugger was entered as a result of a
1343 .It Dv kdb.enter.mac
1344 The kernel debugger was entered as a result of an assertion failure in the
1347 TrustedBSD MAC Framework.
1348 .It Dv kdb.enter.ndis
1349 The kernel debugger was entered as a result of an
1352 .It Dv kdb.enter.netgraph
1353 The kernel debugger was entered as a result of a
1356 .It Dv kdb.enter.panic
1359 .It Dv kdb.enter.powerfail
1360 The kernel debugger was entered as a result of a powerfail NMI on the sparc64
1362 .It Dv kdb.enter.powerpc
1363 The kernel debugger was entered as a result of an unimplemented interrupt
1364 type on the powerpc platform.
1365 .It Dv kdb.enter.sysctl
1366 The kernel debugger was entered as a result of the
1369 .It Dv kdb.enter.trapsig
1370 The kernel debugger was entered as a result of a trapsig event on the sparc64
1372 .It Dv kdb.enter.unionfs
1373 The kernel debugger was entered as a result of an assertion failure in the
1375 .It Dv kdb.enter.unknown
1376 The kernel debugger was entered, but no reason has been set.
1377 .It Dv kdb.enter.vfslock
1378 The kernel debugger was entered as a result of a VFS lock violation.
1379 .It Dv kdb.enter.watchdog
1380 The kernel debugger was entered as a result of a watchdog firing.
1381 .It Dv kdb.enter.witness
1382 The kernel debugger was entered as a result of a
1387 In the event that none of these scripts is found,
1389 will attempt to execute a default script:
1390 .Bl -tag -width kdb.enter.powerfail
1391 .It Dv kdb.enter.default
1392 The kernel debugger was entered, but a script exactly matching the reason for
1393 entering was not defined.
1394 This can be used as a catch-all to handle cases not specifically of interest;
1396 .Dv kdb.enter.witness
1397 might be defined to have special handling, and
1398 .Dv kdb.enter.default
1399 might be defined to simply panic and reboot.
1402 On machines with an ISA expansion bus, a simple NMI generation card can be
1403 constructed by connecting a push button between the A01 and B01 (CHCHK# and
1405 Momentarily shorting these two fingers together may cause the bridge chipset to
1406 generate an NMI, which causes the kernel to pass control to
1408 Some bridge chipsets do not generate a NMI on CHCHK#, so your mileage may vary.
1409 The NMI allows one to break into the debugger on a wedged machine to
1411 Other bus' bridge chipsets may be able to generate NMI using bus specific
1414 Header files mention in this manual page can be found below
1424 .Pa netinet/in_pcb.h
1446 debugger was developed for Mach, and ported to
1448 This manual page translated from
1451 .An Garrett Wollman .
1453 .An Robert N. M. Watson