1 .\" FreeBSD version Copyright (c) 1996
2 .\" Mike Pritchard <mpp@FreeBSD.org>. All rights reserved.
4 .\" Adapted from share/man/man8/man8.hp300/crash.8
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40 .Nd FreeBSD system failures
42 This section explains a bit about system crashes
43 and (very briefly) how to analyze crash dumps.
45 When the system crashes voluntarily it prints a message of the form
46 .Bl -diag -offset indent
47 .It "panic: why i gave up the ghost"
50 on the console, and if dumps have been enabled (see
52 takes a dump on a mass storage peripheral,
53 and then invokes an automatic reboot procedure as
56 Unless some unexpected inconsistency is encountered in the state
57 of the file systems due to hardware or software failure, the system
58 will then resume multi-user operations.
60 The system has a large number of internal consistency checks; if one
61 of these fails, then it will panic with a very short message indicating
63 In many instances, this will be the name of the routine which detected
64 the error, or a two-word description of the inconsistency.
65 A full understanding of most panic messages requires perusal of the
66 source code for the system.
68 The most common cause of system failures is hardware failure, which
69 can reflect itself in different ways.
70 Here are the messages which
71 are most likely, with some hints as to causes.
72 Left unstated in all cases is the possibility that hardware or software
73 error produced the message in some unexpected way.
76 .It "cannot mount root"
77 This panic message results from a failure to mount the root file system
78 during the bootstrap process.
79 Either the root file system has been corrupted,
80 or the system is attempting to use the wrong device as root file system.
81 Usually, an alternate copy of the system binary or an alternate root
82 file system can be used to bring up the system to investigate.
84 this is done by the use of the boot floppy you used to install the system,
90 This is not a panic message, as reboots are likely to be futile.
91 Late in the bootstrap procedure, the system was unable to locate
92 and execute the initialization process,
94 The root file system is incorrect or has been corrupted, or the mode
97 forbids execution or is totally missing.
99 .It "ffs_realloccg: bad optim"
100 .It "ffs_valloc: dup alloc"
101 .It "ffs_alloccgblk: cyl groups corrupted"
102 .It "ffs_alloccg: map corrupted"
103 .It "blkfree: freeing free block"
104 .It "blkfree: freeing free frag"
105 .It "ifree: freeing free inode"
106 These panic messages are among those that may be produced
107 when file system inconsistencies are detected.
108 The problem generally results from a failure to repair damaged file systems
109 after a crash, hardware failures, or other condition that should not
111 A file system check will normally correct the problem.
113 .It "timeout table full"
114 This really should not be a panic, but until the data structure
115 involved is made to be extensible, running out of entries causes a crash.
116 If this happens, make the timeout table bigger.
118 .\" .It "trap type %d, code = %x, v = %x"
119 .\" An unexpected trap has occurred within the system; the trap types are:
120 .\" .Bl -column xxxx -offset indent
123 .\" 2 illegal instruction
125 .\" .No 4\t Em chk No instruction
126 .\" .No 5\t Em trapv No instruction
127 .\" 6 privileged instruction
130 .\" 9 simulated software interrupt
132 .\" 11 FP coprocessor fault
133 .\" 12 coprocessor fault
137 .\" The favorite trap type in system crashes is trap type 8,
138 .\" indicating a wild reference.
139 .\" ``code'' (hex) is the concatenation of the
142 .\" (see <hp300/cpu.h>)
143 .\" in the high 16 bits and the 68020 special status word
144 .\" (see the 68020 manual, page 6-17)
146 .\" ``v'' (hex) is the virtual address which caused the fault.
147 .\" Additionally, the kernel will dump about a screenful of semi-useful
149 .\" ``pid'' (decimal) is the process id of the process running at the
150 .\" time of the exception.
151 .\" Note that if we panic in an interrupt routine,
152 .\" this process may not be related to the panic.
153 .\" ``ps'' (hex) is the 68020 processor status register ``ps''.
154 .\" ``pc'' (hex) is the value of the program counter saved
155 .\" on the hardware exception frame.
158 .\" be the PC of the instruction causing the fault.
159 .\" ``sfc'' and ``dfc'' (hex) are the 68020 source/destination function codes.
160 .\" They should always be one.
161 .\" ``p0'' and ``p1'' are the
163 .\" region registers.
164 .\" They are of the form:
166 .\" .Bd -ragged -offset indent
167 .\" <length> '@' <kernel VA>
170 .\" where both are in hex.
171 .\" Following these values are a dump of the processor registers (hex).
172 .\" Finally, is a dump of the stack (user/kernel) at the time of the offense.
174 .It "init died (signal #, exit #)"
175 The system initialization process has exited with the specified
176 signal number and exit code.
177 This is bad news, as no new users will then be able to log in.
178 Rebooting is the only fix, so the
179 system just does it right away.
182 That completes the list of panic types you are likely to see.
184 If the system has been configured to take crash dumps (see
186 then when it crashes it will write (or at least attempt to write)
187 an image of memory into the back end of the dump device,
188 usually the same as the primary swap
190 After the system is rebooted, the program
192 runs and preserves a copy of this core image and the current
193 system in a specified directory for later perusal.
198 To analyze a dump you should begin by running
199 .Xr kgdb 1 Pq Pa ports/devel/gdb
200 on the system load image and core dump.
201 If the core image is the result of a panic,
202 the panic message is printed.
203 For more details consult the chapter on kernel debugging in
205 .%B "FreeBSD Developers' Handbook"
206 .Pq Pa https://www.freebsd.org/doc/en/books/developers-handbook/ .
208 .Xr kgdb 1 Pq Pa ports/devel/gdb ,
215 manual page first appeared in