Debug using gdb for Apache
pstack is this quite an interesting tool for debugging in case you don’t want to trace the server. Basically this command command shows a stack trace for each process!! Similar to gstack but for RHEL.
Example stolen from Oracle to demonstrate nfsd
243: /usr/lib/nfs/nfsd -a 16 ef675c04 poll (24d50, 2, ffffffff) 000115dc ???????? (24000, 132c4, 276d8, 1329c, 276d8, 0) 00011390 main (3, efffff14, 0, 0, ffffffff, 400) + 3c8 00010fb0 _start (0, 0, 0, 0, 0, 0) + 5c
On this case we can see that last function is pool, called from ??? – without ELF info – which was called by main.
The reading follows the simple rule:
The bottom is the start –> the top is the last call