Getting A Backtrace
Sometimes PHP will spin at 100% CPU and it is difficult to figure out why. The `strace` command is too noisy, and without knowing where in the code there is a problem, you cannot insert your own backtrace. The newer version of WHM has support for multiple PHP versions, so make sure you run this for whatever PHP version the site is using. In our case, this is using php-fpm.
First, install xdebug:
/opt/cpanel/ea-php72/root/usr/bin/pecl install xdebug
After that, follow the instructions here: https://stackoverflow.com/questions/14261821/get-a-stack-trace-of-a-hung-php-script#53056294
Basically you just need to run the following:
gdb --batch --readnever --pid=$pid --command=/tmp/dumpstack.gdbscript
And the content of dumpstack.gdbscript is:
set $xstack = ((long**)&xdebug_globals)[2]
if ($xstack !=0) && ($xstack[0]!=0)
set $pcurrent = (long*)$xstack[0]
while $pcurrent
set $xptr = (long*)$pcurrent[0]
set $xptr_s = (char**)$xptr
set $xptr_i = (int*)$xptr
set $filename = $xptr_s[4]
set $funcname = $xptr_s[1]
set $linenum = $xptr_i[10]
if ($funcname!=0)
printf "%s@%s:%d\\n", $funcname, $filename, $linenum
else
printf "global@%s:%d\\n", $filename, $linenum
end
set $pnext = (long*)$pcurrent[2]
set $pcurrent = $pnext
end
else
printf "no stack"
end