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From Yann Ylavic <>
Subject Re: [users@httpd] Lots of messages "[ssl:warn] Resource deadlock avoided: AH02026: Failed to acquire SSL session cache lock"
Date Thu, 10 Mar 2016 13:08:14 GMT
On Thu, Mar 10, 2016 at 11:09 AM, Hildegard Meier <> wrote:
> Reading
> I guess, expected behaviour of active directive
> Mutex file:${APACHE_LOCK_DIR} default

Does it come from Ubuntu?
If so, I don't any modern Linux should configure the "file" mutex
mechanism by default, and you could possibly report it...

> would be
> Mutex fnctl:${APACHE_LOCK_DIR} default
> ?
> Maybe it's worth a try to add the line
> Mutex fnctl:${APACHE_LOCK_DIR} ssl-cache

Honestly I don't know how "fnctl" works on Linux, but I'd recommend
using no Mutex directive at all (same as "Mutex default") which falls
back to "Mutex sysvsem default" given your output of apachectl (i.e.
"-D APR_USE_SYSVSEM_SERIALIZE"), or possibly "Mutex pthread default"
which is the most efficient on Linux IMHO (also robust, leaks free on

> and look if
> /var/lock/apache2/ssl-cache
> gets created

Both suggested mechanisms above are not file backed, "sysvsem" can be
seen with the "ipcs -s" command and "pthread" is (shared-)memory only.

> and the
> "AH02026: Failed to acquire SSL session cache lock" messages disappear?

Hopefully, the "file" mechanism is not suitable anyway or modern OS.

> But we need to test that on our standby server after upgrading that to Apache 2.4 which
will be done in 10 days or so.

Good idea :)


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