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Computer And Technologies: Ho will you detect SNMP crash or core dump ?

Tuesday, 10 November 2009

Ho will you detect SNMP crash or core dump ?

How will you detect or how to debug where the core dump occures?
Please follow the steps:-

GDB is the GNU debugger, which is a terminal-based debugger. DDD is a graphical (GUI) front end to GDB.

Normal invocation

The simplest way to run an application under GDB is like so:

$ gdb /usr/local/sbin/snmpd
(gdb) run -f -Lo

The '-f' is necessary to prevent snmpd from forking into the background, and '-Lo' tells snmpd to send log messages to STDOUT (i.e. print them in the GDB console window).

Libtool invocation

Net-SNMP uses libtool while building it's applications. This means that sometimes the applications in the source/build directory are not actually binaries, but shell scripts. The libtool script does some magic so that the applications will run using the shared libraries in the build directory, instead of any libraries installed on the system. To run an application with GDB, you have to run GDB through libtool, like so:

$ ./libtool gdb agent/snmpd
(gdb) run -f -Lo

Getting a backtrace (aka stack trace)

Once you have got an application running under GDB, you can easily get a backtrace, which will display the sequence of functions that were called to arrive at the point where the debugger is currently stopped.

(gdb) bt
#0 0x10153d78 in init_snmp(type=0x101bb140 "snmp") at snmp_api.c:854
#1 0x1000524c in main(argc=3, argv=0x7fe04636) at snmpd.c:910
If an application has crashed, often it will leave a core file. This core file can usually be loaded into GDB to get debugging information after the fact. Simply add the path to the core file after the path to the application when starting GDB.
$ gdb /usr/local/sbin/snmpd /tmp/core.70816

Often this will tell you why the application crashed (e.g. SIGSEGV, aka signal 11). You can then get a backtrace to send to one of the mailing lists for interpretation.

If testing snmpd (or another application) from within the source tree, you'll need to run gdb via libtool:

$ ./libtool gdb agent/snmpd /tmp/core.70816

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