apache logs:
[Thu Dec 31 12:27:41 2009] [notice] child pid 19818 exit signal Bus error (7)

The first error “Bus Error” is caused by someones (possibly CGI) program crashing. A bus error happens when someone wrote a C program for Intel and re-compiled it for another processor like PPC or Mips that does not support misalligned memory access. Really all it means is someone is running buggy software on your server machine.
The second error could also be a CGI program that hangs longer than the server’s timeout, so its killed. Probably another buggy program.

That sounds like bad RAM or maybe a bad chassis. I would try and build something other the Apache and see if you get similar errors. If they persist then I would ask for a RAM swap to be done and check again. If that does not fix it then request a chassis swap.

There is a small chance this could be OS related if you are running a different Kernel release compared to the OS default or have many patches installed on it but I am leaning towards a hardware issue.

http://www.kernel.org/doc/man-pages/online/pages/man7/signal.7.html

Standard Signals

       Linux supports the standard signals listed below.  Several signal numbers are
       architecture-dependent, as indicated in the “Value” column.  (Where three
       values are given, the first one is usually valid for alpha and sparc, the
       middle one for ix86, ia64, ppc, s390, arm and sh, and the last one for mips.
       A – denotes that a signal is absent on the corresponding architecture.)

       First the signals described in the original POSIX.1-1990 standard.

       Signal     Value     Action   Comment

       ———————————————————————-
       SIGHUP        1       Term    Hangup detected on controlling terminal
                                     or death of controlling process
       SIGINT        2       Term    Interrupt from keyboard
       SIGQUIT       3       Core    Quit from keyboard
       SIGILL        4       Core    Illegal Instruction
       SIGABRT       6       Core    Abort signal from abort(3)
       SIGFPE        8       Core    Floating point exception
       SIGKILL       9       Term    Kill signal
       SIGSEGV      11       Core    Invalid memory reference
       SIGPIPE      13       Term    Broken pipe: write to pipe with no
                                     readers
       SIGALRM      14       Term    Timer signal from alarm(2)
       SIGTERM      15       Term    Termination signal
       SIGUSR1   30,10,16    Term    User-defined signal 1
       SIGUSR2   31,12,17    Term    User-defined signal 2
       SIGCHLD   20,17,18    Ign     Child stopped or terminated
       SIGCONT   19,18,25    Cont    Continue if stopped
       SIGSTOP   17,19,23    Stop    Stop process
       SIGTSTP   18,20,24    Stop    Stop typed at tty
       SIGTTIN   21,21,26    Stop    tty input for background process
       SIGTTOU   22,22,27    Stop    tty output for background process

       The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

       Next the signals not in the POSIX.1-1990 standard but described in SUSv2 and
       POSIX.1-2001.

       Signal       Value     Action   Comment
       ——————————————————————–
       SIGBUS      10,7,10     Core    Bus error (bad memory access)
       SIGPOLL                 Term    Pollable event (Sys V).
                                       Synonym for SIGIO
       SIGPROF     27,27,29    Term    Profiling timer expired
       SIGSYS      12,-,12     Core    Bad argument to routine (SVr4)
       SIGTRAP        5        Core    Trace/breakpoint trap
       SIGURG      16,23,21    Ign     Urgent condition on socket (4.2BSD)
       SIGVTALRM   26,26,28    Term    Virtual alarm clock (4.2BSD)
       SIGXCPU     24,24,30    Core    CPU time limit exceeded (4.2BSD)
       SIGXFSZ     25,25,31    Core    File size limit exceeded (4.2BSD)

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