Why can't I dtrace processes running in a jail from the host?

Patrick M. Hausen hausen at punkt.de
Thu Aug 16 07:25:41 UTC 2018

Good morning,

I did some further investigation and with help from Mark was
finally able to get it working.

Took quite some effort - documentation on the PHP side - NULL :-/
BTW: has anyone ever successfully subscribed to one of the PHP
mailing lists? Where is the community of the people developing that

OK, back to topic, in fact I had two issues, one FreeBSD, one PHP

1.	DTrace'ing jailed userland probes requires /dev/dtrace/* to
	be visible inside the jail.


	add include $devfsrules_jail
	add path dtrace/* unhide

	iocage set devfs_ruleset=100 vpro0069

Voila - dtrace on the host, watch userland probes in the jail.

2.	PHP > 5.6 needs the environment variable USE_ZEND_DTRACE
	to be set to register it's probes.

Turned out that it was not sufficient to *configure* that into the PHP
FPM worker but you need to set (and export) the variable on the shell
before you start the FPM master daemon. Then everything works as expected.

What I regularly do in such a case is

	sh -x /usr/local/etc/rc.d/php-fpm start

to find out what command is actually executed in the end. Then call that directly
after setting the environment. Result:

	limits -C daemon /usr/local/sbin/php-fpm

Bingo! Surprisingly enough it is *not* necessary to configure

	clear_env = no

in PHP FPM ... DTrace is active as soon as the master daemon sees that
environment variable.

Kind regards
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