Get a stack trace of a running or hung PHP script

Question

I have a script that runs from a cron job every night. Recently, it has started totally freezing up after several minutes into the script, and I can't figure out why. If this was Java, I could simply run kill -3 PID and it would print a thread dump in stdout. Is there any equivalent in PHP, where I could get a dump of the current stack trace (and ideally memory info) on a running PHP script?

Answer 1

The best thing you can do is compile PHP yourself using --enable-debug during configure. If the process then still hangs you can use gdb and some macros to get a PHP-level stacktrace using these steps:

$ gdb -p $PHP_PID
(gdb) bt     # Get a system-level stacktrace, might already give some info
(gdb) source /path/to/php-src/.gdbinit # Load some useful macros
(gdb) dump_bt executor_globals.current_execute_data
            # Macro from PHP's .gbinit giving PHP stack trace
            # If you for whatever reason are using a thread-safe PHP build you have to do this:
(gdb) ____executor_globals
(gdb) dump_bt $eg.current_execute_data

And then debug ahead :-)

Note that for this to work you have to have a PHP binary with symbol information, --enable-debug ensures that.