HOW TO HANDLE CORE DUMPS ON UNIX

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Problem: HOW TO HANDLE CORE DUMPS ON UNIX


Symptoms:

A core dump is an image copy of the state of a process, which is produced if
the process attempts to do something not allowed by the Operating System. The process information is written to a file named "core", which is usually
created in the current working directory of the process.

Some of the things a program might attempt to do that would cause a core dump
include: trying to execute an illegal/unknown instruction, trying to access
memory outside the allowed range, or trying to use an unavailable resource.

A core file contains much information to aid in determining why a process
crashed. One of the things contained in a core file is a called stack trace,
which identifies what commands a process has, or was attempting to execute.

Sometimes a trace file is automatically produced by an Oracle process, and is
normally indicated with an ORA-07445 error. When this occurs, a file with the extension ".trc" will be produced. To find this file, check your
init.ora for the parameters "user_dump_dest" and "background_dump_dest".
The trace file will typically be located in one of these directories.

A trace file is not always produced automatically, and the solution of this
article will discuss how to manually produce a call stack trace.


Search Words:
=============

segmentation fault
ORA-7445
dbx gdb dde adb sdb debug
debugger


Log files:



Solution:



Before attempting to manually create a stack trace from a core file, please
verify the following:

* Your swap space is 2 to 3 times the amount of physical memory (RAM)
installed on the system, or whichever is greater of the following
2 items: 1GB or 2 times the size of all SGAs combined.

You can approximate the size of an SGA with this formula:

((db_block_size * db_block_buffers)+shared_pool+log_buffers)/.9

For help with how to check swap space, refer to PRE 1016233.6.


* You are using a supported compiler/linker. Check the Installation
Guide for Operating System requirements.

NOTE: On Solaris systems, make sure that "/usr/ccs/bin" is
before "/usr/ucb" in the PATH environment variable.
You can confirm this using the following command:

% which ld

The path returned should be "/usr/ccs/bin/ld".


* You have at least 50MB of free space available in "/tmp".


Creating a Stack Trace from a Core File
=======================================

To create a stack trace from a core file, perform the following steps:

1. Determine which executable program caused the core dump:

To determine which executable caused a core dump, change to the
directory where the core file is located, and use the "file"
command.

For example, if you had a core file in your home directory,
"/home/user", use the following commands:

% cd /home/user
% file core

core: ELF 32-bit MSB core file SPARC Version 1, from 'sqlplus'

The "from" information indicates that 'sqlplus' caused the core
dump.

(a) If your system does not display "from" information when using
the "file" command, and your are NOT using SCO UNIX, try the
following command instead:

% cd /home/user
% strings core | head -10

CORE
CORE
CORE
sqlplus <<----- first executable program sqlplus -h system-23_getm TERM=xterms console ORACLE_HOME guicommon/tk2 /SQLPlus/mesg/SP2US.msb This will display the first 10 text entries in the core file. Start at the first line and look for an entry which is an executable program. In the example above, 'sqlplus' caused the core dump. (b) If you are using SCO UNIX, use the following command instead: % cd /home/user % strings core | head -75 | tail -25 2. Determine which debugger exists on your system. There are many different debuggers in the UNIX world. Look at the list below of the most common debuggers, then check your system for one of them. Common debuggers ================ dbx, gdb, dde, adb, sdb, debug If these debuggers exist on your system, they would most likely be located in one of the following directories: /bin, /usr/bin, /opt/langtools/bin, /usr/ccs/bin, /usr/ucb To search your system for a debugger, you can use the "which" command, which will search only the directories in your current PATH, or the "find" command, which can search the entire system. For example, to search for the dbx debugger: % which dbx no dbx ... % find / -name "dbx" -print /usr/ccs/bin/dbx 3. Now that you have located a debugger, you are ready to use it to produce the stack trace. The Unix command "script" will capture the output of a terminal session and write it to a file. You will use "script" to capture the output of the debugger as shown below. First change directories to the location where the core file is located. 4. The next step depends upon which debugger you are using: (a) If you are NOT using the "dde" or "debug" debugger, do this: ------------------------------------------------------------ % script mystack.trc % $ORACLE_HOME/bin/ core

where is the debugger you are using, and
is the executable program which caused the core dump.


(b) If you are using the "dde" debugger, use this command:
------------------------------------------------------

% script mystack.trc
% dde -ui line core $ORACLE_HOME/bin/


(c) If you are using the "debug" debugger, use this command:
--------------------------------------------------------

% script mystack.trc
% debug -c core $ORACLE_HOME/bin/

where is not entered, unless "debug" starts
an X window session, in which case equals
"-i c".


5. Now look at the table below and find your debugger in the first
column, then enter the command in the second column to produce the
stack trace.

debugger command to produce stack
======== ========================
dbx where
gdb bt
dde tb
adb $c
sdb t
debug stack


6. Exit the debugger program:

- if you are using the "adb" debugger, exit using -D

- if you are using any of the other debuggers, exit with the
command "q"


7. After exiting the debugger, issue the command "exit" at the shell
prompt. You should receive a "Script Done" message.


You now have a stack trace in the file named "mystack.trc", and you can send
this file to Oracle Support for further analysis.


Solution Explanation:
=====================

The call stack trace in the "mystack.trc" file can be useful to Oracle Support
in determining why a core dump from an Oracle product occurred.


References:

HOW TO HANDLE CORE DUMPS ON UNIX [ID 1007808.6]

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