Upgrading from 2.2 to 2.4 somehow mpm_itk was enabled along wiuth mpm_prefork. This problem was discussed in an\my earlier thread : constant mpm_itk errors in Apache error log This resulted in the "mpm_itk errors" going but now I am getting these core notices instead : [core:notice] [pid xxxxx] AH00052: child pid 4597 exit signal Segmentation fault (11) Does anyone know what I should be looking at to finally fix this?


I managed to strace a process right through to its segfault, but cant really interpret it. Any help would be greatly appreciated:

rt_sigprocmask(SIG_UNBLOCK, [PROF], NULL, 8) = 0
getcwd("/", 4095)                       = 2
chdir("/website/public")                = 0
lstat("/website/public/index.php", {st_mode=S_IFREG|0644, st_size=1777, ...}) = 0
lstat("/website/public", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/website", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
setitimer(ITIMER_PROF, {it_interval={0, 0}, it_value={30, 0}}, NULL) = 0
fcntl(14, F_SETLK, {type=F_RDLCK, whence=SEEK_SET, start=1, len=1}) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR,        si_addr=0x7f5a3d942028} ---
chdir("/etc/apache2")                   = 0
rt_sigaction(SIGSEGV, {SIG_DFL, [], SA_RESTORER|SA_INTERRUPT, 0x7f5a3cd258d0}, {SIG_DFL, [], SA_RESTORER|SA_RESETHAND, 0x7f5a3cd258d0}, 8) = 0
kill(24177, SIGSEGV)                    = 0
rt_sigreturn()                          = 140025556901856
--- SIGSEGV {si_signo=SIGSEGV, si_code=SI_USER, si_pid=24177, si_uid=33} ---
+++ killed by SIGSEGV +++
  • strace or gdb would be my first port of call. – womble Aug 10 '15 at 23:52
  • Thanks womble. I'll have to read up and experiment Locally on them first as they look a bit 'scary' to dive straight into on my live ecommerce site. – Daryl Aug 11 '15 at 0:05
  • Ok, I used strace to track one of the processes right through to its segfault, but I haven't really got a clue how to read it. Again, any advice would be greatly appreciated: – Daryl Aug 11 '15 at 21:51
  • Sometimes you get lucky and strace gives you a hint; time for some gdb action. Chances are you'll need to install debugging symbols for Apache to make any sense out of it. – womble Aug 11 '15 at 22:45
  • Thanks for looking. Nothing worthwhile hey? Oh well,looks like tonights project will be gdb. Will keep updating my original post until I finally solve this... – Daryl Aug 11 '15 at 23:26

The strace command lists the systemcalls the application make as it is running.

If you're not de developer: Section 2 of the system manual documents system calls helping you understand what is happening.

fcntl(14, F_SETLK, {type=F_RDLCK, whence=SEEK_SET, start=1, len=1}) = 0

man 2 fcntl

Name fcntl - manipulate file descriptor

int fcntl(int fd, int cmd, ... /* arg */ );

fcntl() performs one of the operations described below on the open file descriptor fd. The operation is determined by cmd.
fcntl() can take an optional third argument. Whether or not this argument is required is determined by cmd. The required argument type is indicated in parentheses after each cmd name (in most cases, the required type is int, and we identify the argument using the name arg), or void is specified if the argument is not required. ...

In other words: a read-lock is attempted on file-descriptor number 14. To find out which file that is there should be symbolic link with the number 14, the integer representing the file in /proc/<PID>/fd/14.

To my eye that looks unrelated to the error in the next line but I'm no developer...:

--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR, si_addr=0x7f5a3d942028} ---

si_signo=SIGSEGV looks like the process id your were monitoring received the segmentation fault (SIGSEGV) signal caused by accessing an invalid memory address, 0x7f5a3d942028, an address which it isn't allowed to access (the SEGV_ACCERR si_code).

As to why that happened: strace is often unlikely to help you there.

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