# The path for core dump is like this: /i-data/md0/.system/core.*.
# The path pattern is written in /proc/sys/kernel/core_pattern.
cat /proc/sys/kernel/core_pattern
/i-data/md0/.system/core.%e.%u.%g.%s

# In order to generate core dump declare in php-fpm.conf:
rlimit_core = unlimited

# reading php-fpm's core dump:
gdb /ffp/sbin/php-fpm /i-data/md0/.system/core.php-fpm.99.99.11
#the output is below (the problem seems to be zend_hash_internal_pointer_reset_ex):
    Program terminated with signal SIGSEGV, Segmentation fault.
    #0  0x003c7898 in zend_hash_internal_pointer_reset_ex ()
#in gdb console you could analyze other core dump file with:
target core /i-data/md0/.system/core.php-fpm.99.99.11
#additional info with backtrace command
backtrace
    #0  0x003c7898 in zend_hash_internal_pointer_reset_ex ()
    #1  0x412026b4 in ps_srlzr_decode_msgpack () from /ffp/lib/php/extensions/no-debug-zts-20131226/msgpack.so
    #2  0x00238248 in ?? ()
    Backtrace stopped: previous frame identical to this frame (corrupt stack?)
#x command on #2 0x00238248 address
x 0x00238248
quit -> for exiting from gdb console

#when gallery3 fails with core dump on php-fpm than recompile msgpack
#see https://adrhc.go.ro/wordpress/configure-command-for-building-various-software/
#Strange: gallery3 fails with core dump in msgpack only when using chrome!

# http://linux.die.net/man/1/strace
# http://forum.nas-central.org/viewtopic.php?f=249&t=15891&start=30
nohup /ffp/bin/strace -o $HOME/temp/strace-updatedb.log /ffp/bin/updatedb --prunepaths='/dev /e-data /ffp /i-data/60cb70cf/.zyxel/zy-pkgs /i-data/md0/.zyxel/zy-pkgs /init /linuxrc /mnt /proc /ram_bin /srv /sys /usr/local/zy-pkgs/ffproot/ffp/var /var' &