panic - what happens when the system crashes
This section explains what happens when the system crashes and how you
can analyze crash dumps.
When the system crashes voluntarily, it displays a message of the form
panic: why i gave up the ghost
on the console, takes a dump on a mass storage peripheral, and then
invokes an automatic reboot procedure as described in reboot(8).
Unless some unexpected inconsistency is encountered in the state of the
file systems due to hardware or software failure, the system will then
resume multiuser operations.
The system has a large number of internal consistency checks; if one of
these fails, it will panic with a very short message indicating which
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, you can run the program savecore(8) to preserve a
copy of this core image and kernel namelist for later perusal. See
savecore(8) for details.
To analyze a dump you should begin by running adb(1) with the -k flag
on the core dump, as described in
The most common cause of system failures is hardware failure, which can
reflect itself in different ways.
See DIAGNOSTICS for some messages that you may encounter, with some
hints as to causes. In each case there is a possibility that a hard-
ware or software error produced the message in some unexpected way.
/vmunix the system kernel
/etc/rc.local script run when the local system starts up
adb(1), old-analyze(8), reboot(8) sa(8), savecore(8)
IO err in push
hard IO err in swap
The system encountered an error trying to write to the pag-
ing device or an error in reading critical information from
a disk drive. You should fix your disk if it is broken or
timeout table overflow
This really should not be a panic, but until the data
structure is fixed, involved, running out of entries causes
a crash. If this happens, you should make the timeout ta-
ble bigger by changing the value of ncallout in the param.c
file, and then rebuild your system.
trap type type, pid process-id, pc = program-counter, sr = status-reg-
ister, context context-number
A unexpected trap has occurred within the system; typical
trap types are:
o Bus error
o Address error
o Illegal instruction
o Divide by zero
o Chk instruction
o Trapv instruction
o Privilege violation
o 1010 emulator trap
o 1111 emulator trap
o Stack format error
o Uninitialized interrupt
o Spurious interrupt
The favorite trap types in system crashes are ``Bus error''
or ``Address error'', indicating a wild reference. The
process-id is the ID of the process running at the time of
the fault, program-counter is the hexadecimal value of the
program counter, status-register is the hexadecimal value
of the status register, and context-number is the context
that the process was running in. These problems tend to be
easy to track down if they are kernel bugs since the pro-
cessor stops cold, but random flakiness seems to cause this
init died The system initialization process has exited. This is bad
news, as no new users will then be able to log in. Reboot-
ing is the only fix, so the system just does it right away.
25 September 1987 PANIC(8S)