[unix-history] / usr / man / man8 / crash.8v

.TH CRASH 8V "1 September 1981"
.UC 4
.SH NAME
crash \- what happens when the system crashes
.SH DESCRIPTION
This section explains what happens when the system crashes and how
you can analyze crash dumps.
.PP
When the system crashes voluntarily it prints a message of the form
.IP
panic: why i gave up the ghost
.LP
on the console, takes a dump on a mass storage peripheral,
and then invokes an automatic reboot procedure as
described in
.IR reboot (8).
(If auto-reboot is disabled on the front panel of the machine the system
will simply halt at this point.)
Unless some unexpected inconsistency is encountered in the state
of the file systems due to hardware or software failure the system
will then resume multi-user operations.
.PP
The system has a large number of internal consistency checks; if one
of these fails, then it will panic with a very short message indicating
which one failed.
.PP
The most common cause of system failures is hardware failure, which
can reflect itself in different ways.  Here are the messages which
you are likely to encounter, with some hints as to causes.
Left unstated in all cases is the possibility that hardware or software
error produced the message in some unexpected way.
.TP
.B IO err in push
.ns
.TP
.B hard IO err in swap
The system encountered an error trying to write to the paging device
or an error in reading critical information from a disk drive.
You should fix your disk if it is broken or unreliable.
.TP
.B timeout table overflow
.ns
This really shouldn't be a panic, but until we fix up the data structure
involved, running out of entries causes a crash.  If this happens,
you should make the timeout table bigger.
.TP
.B KSP not valid
.ns
.TP
.B SBI fault
.ns
.TP
.B CHM? in kernel
These indicate either a serious bug in the system or, more often,
a glitch or failing hardware.
If SBI faults recur, check out the hardware or call
field service.  If the other faults recur, there is likely a bug somewhere
in the system, although these can be caused by a flakey processor.
Run processor microdiagnostics.
.TP
.B machine check %x:
.I description
.ns
.TP
.I \0\0\0machine dependent machine-check information
.ns
We should describe machine checks, and will someday.
For now, ask someone who knows (like your friendly field service people).
.TP
.B trap type %d, code=%d, pc=%x
A unexpected trap has occurred within the system; the trap types are:
.sp
.nf
0	reserved addressing fault
1	privileged instruction fault
2	reserved operand fault
3	bpt instruction fault
4	xfc instruction fault
5	system call trap
6	arithmetic trap
7	ast delivery trap
8	segmentation fault
9	protection fault
10	trace trap
11	compatibility mode fault
12	page fault
13	page table fault
.fi
.sp
The favorite trap types in system crashes are trap types 8 and 9,
indicating
a wild reference.  The code is the referenced address, and the pc at the
time of the fault is printed.  These problems tend to be easy to track
down if they are kernel bugs since the processor stops cold, but random
flakiness seems to cause this sometimes.
.TP
.B init died
The system initialization process has exited.  This is bad news, as no new
users will then be able to log in.  Rebooting is the only fix, so the
system just does it right away.
.PP
That completes the list of panic types you are likely to see.
.PP
When the system crashes it writes (or at least attempts to write)
an image of memory into the back end of the primary swap
area.  After the system is rebooted, the program
.IR savecore (8)
runs and preserves a copy of this core image and the current
system in a specified directory for later perusal.  See
.IR savecore (8)
for details.
.PP
To analyze a dump you should begin by running
.IR adb (1)
with the 
.B \-k
flag on the core dump.
Normally the command
``*(intstack-4)$c''
will provide a stack trace from the point of
the crash and this will provide a clue as to
what went wrong.
A more complete discussion
of system debugging is impossible here.
See, however,
``Using ADB to Debug the UNIX Kernel''.
.SH "SEE ALSO"
adb(1),
analyze(8),
reboot(8)
.br
.I "VAX 11/780 System Maintenance Guide"
for more information about machine checks.
.br
.I "Using ADB to Debug the UNIX Kernel"
Commit	Line	Data
e7839a72 C	1	.TH CRASH 8V "1 September 1981"
	2	.UC 4
	3	.SH NAME
	4	crash \- what happens when the system crashes
	5	.SH DESCRIPTION
	6	This section explains what happens when the system crashes and how
	7	you can analyze crash dumps.
	8	.PP
	9	When the system crashes voluntarily it prints a message of the form
	10	.IP
	11	panic: why i gave up the ghost
	12	.LP
	13	on the console, takes a dump on a mass storage peripheral,
	14	and then invokes an automatic reboot procedure as
	15	described in
	16	.IR reboot (8).
	17	(If auto-reboot is disabled on the front panel of the machine the system
	18	will simply halt at this point.)
	19	Unless some unexpected inconsistency is encountered in the state
	20	of the file systems due to hardware or software failure the system
	21	will then resume multi-user operations.
	22	.PP
	23	The system has a large number of internal consistency checks; if one
	24	of these fails, then it will panic with a very short message indicating
	25	which one failed.
	26	.PP
	27	The most common cause of system failures is hardware failure, which
	28	can reflect itself in different ways. Here are the messages which
	29	you are likely to encounter, with some hints as to causes.
	30	Left unstated in all cases is the possibility that hardware or software
	31	error produced the message in some unexpected way.
	32	.TP
	33	.B IO err in push
	34	.ns
	35	.TP
	36	.B hard IO err in swap
	37	The system encountered an error trying to write to the paging device
	38	or an error in reading critical information from a disk drive.
	39	You should fix your disk if it is broken or unreliable.
	40	.TP
	41	.B timeout table overflow
	42	.ns
	43	This really shouldn't be a panic, but until we fix up the data structure
	44	involved, running out of entries causes a crash. If this happens,
	45	you should make the timeout table bigger.
	46	.TP
	47	.B KSP not valid
	48	.ns
	49	.TP
	50	.B SBI fault
	51	.ns
	52	.TP
	53	.B CHM? in kernel
	54	These indicate either a serious bug in the system or, more often,
	55	a glitch or failing hardware.
	56	If SBI faults recur, check out the hardware or call
	57	field service. If the other faults recur, there is likely a bug somewhere
	58	in the system, although these can be caused by a flakey processor.
	59	Run processor microdiagnostics.
	60	.TP
	61	.B machine check %x:
	62	.I description
	63	.ns
	64	.TP
65	.I \0\0\0machine dependent machine-check information
66	.ns
67	We should describe machine checks, and will someday.
68	For now, ask someone who knows (like your friendly field service people).
69	.TP
70	.B trap type %d, code=%d, pc=%x
71	A unexpected trap has occurred within the system; the trap types are:
72	.sp
73	.nf
74	0 reserved addressing fault
75	1 privileged instruction fault
76	2 reserved operand fault
77	3 bpt instruction fault
78	4 xfc instruction fault
79	5 system call trap
80	6 arithmetic trap
81	7 ast delivery trap
82	8 segmentation fault
83	9 protection fault
84	10 trace trap
85	11 compatibility mode fault
86	12 page fault
87	13 page table fault
88	.fi
89	.sp
90	The favorite trap types in system crashes are trap types 8 and 9,
91	indicating
92	a wild reference. The code is the referenced address, and the pc at the
93	time of the fault is printed. These problems tend to be easy to track
94	down if they are kernel bugs since the processor stops cold, but random
95	flakiness seems to cause this sometimes.
96	.TP
97	.B init died
98	The system initialization process has exited. This is bad news, as no new
99	users will then be able to log in. Rebooting is the only fix, so the
100	system just does it right away.
101	.PP
102	That completes the list of panic types you are likely to see.
103	.PP
104	When the system crashes it writes (or at least attempts to write)
105	an image of memory into the back end of the primary swap
106	area. After the system is rebooted, the program
107	.IR savecore (8)
108	runs and preserves a copy of this core image and the current
109	system in a specified directory for later perusal. See
110	.IR savecore (8)
111	for details.
112	.PP
113	To analyze a dump you should begin by running
114	.IR adb (1)
115	with the
116	.B \-k
117	flag on the core dump.
118	Normally the command
119	``*(intstack-4)$c''
120	will provide a stack trace from the point of
121	the crash and this will provide a clue as to
122	what went wrong.
123	A more complete discussion
124	of system debugging is impossible here.
125	See, however,
126	``Using ADB to Debug the UNIX Kernel''.
127	.SH "SEE ALSO"
128	adb(1),
129	analyze(8),
130	reboot(8)
131	.br
132	.I "VAX 11/780 System Maintenance Guide"
133	for more information about machine checks.
134	.br
135	.I "Using ADB to Debug the UNIX Kernel"