[squid-users] FATAL: shm_open(/squid-ssl_session_cache.shm)

[Aaron Turner]

Thanks Alex.

So I guess what I'd like to know is how squid handles a multi-layer
cache config with ssl bumping?  For obvious performance reasons, I
don't want to bump the same connection twice.  Much rather have the
first layer bump the connection and have a memory cache.  If that
cache is a miss, then hit the slower disk cache/outbound network
connection.

Thanks,
Aaron
--
Aaron Turner
https://synfin.net/         Twitter: @synfinatic
My father once told me that respect for the truth comes close to being
the basis for all morality.  "Something cannot emerge from nothing,"
he said.  This is profound thinking if you understand how unstable
"the truth" can be.  -- Frank Herbert, Dune


On Fri, Aug 25, 2017 at 3:13 PM, Alex Rousskov
<rousskov at measurement-factory.com> wrote:
> On 08/25/2017 11:21 AM, Aaron Turner wrote:
>> FATAL: Ipc::Mem::Segment::open failed to
>> shm_open(/squid-ssl_session_cache.shm): (2) No such file or directory
>
>> I've verified that /dev/shm is mounted and based on the list of files
>> in there, clearly squid is able to create files there, so it's not a
>> Linux/shm config issue.
>
> Yes, moreover, this is not a segment creation failure. This is a failure
> to open a segment that should exist but is missing. That segment should
> have been created by the master process, but since your config (ab)uses
> SMP macros, I am guessing that depending on the configuration details,
> the master process may not know that it needs to create that segment.
>
> For the record, the same error happens in older Squids (including v3.5)
> when there are two concurrent Squid instances running. However, I
> speculate that you are suffering from a misconfiguration, not broken PID
> file management here.
>
>
>> So here's the funny thing... this worked fine until I enabled
>> ssl-bumping on the backends (I was debugging some problems and on a
>> whim I tried enabling it).  That didn't solve my problem and so I
>> disabled ssl bumping on the backends.  And that's when this SHM error
>> started happening with my frontend.   Re-enabling ssl-bump on the
>> backends fixes the SHM error, but I don't think that would be a
>> correct config?
>
> This is one of the reasons folks should not abuse SMP Squid for
> implementing CARP clusters IMHO -- the config on that wiki page is
> conceptually wrong, even though it may work in some cases.
>
> SMP macros are useful for simple, localized hacks like splitting
> cache.log into worker-specific files or adding worker ID to access.log
> entries. However, the more process-specific changes you introduce, the
> higher are the changes that Squid will get confused.
>
> The overall principle is that all Squid processes should see the same
> configuration. YMMV, but the number of places where SMP Squid relies on
> that principle keeps growing...
>
> Alex.