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From bugzi...@apache.org
Subject [Bug 54415] New: Please tell the root cause of mutex and scoreboard generation failure!
Date Mon, 14 Jan 2013 09:16:30 GMT
https://issues.apache.org/bugzilla/show_bug.cgi?id=54415

            Bug ID: 54415
           Summary: Please tell the root cause of mutex and scoreboard
                    generation failure!
           Product: Apache httpd-2
           Version: 2.4.3
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Core
          Assignee: bugs@httpd.apache.org
          Reporter: jackie.qq.zhang@gmail.com
    Classification: Unclassified

Hi, Apache httpd,

I experienced the following mutex generation error:

[core:emerg] [pid 30875:tid 140406146557696] (28)No space left on device:
AH00023: Couldn't create the rewrite-map mutex
285 AH00016: Configuration Failed

It's weird because I don't have "rewrite-map" related configuration in my
httpd.conf, I even do not know what is a rewrite-map mutex, and what it's used
for. Also, I checked my disk space and filesystem quota but I have plenty of
space.

I tried hard to modify my httpd.conf to make it work but failed. Then, I
searched on the Internet and figured out it's because of orphan semaphores due
to unclean shutdown.

But, I was surprised to see so many people experienced the same problem. Just
randomly grab some of them:

http://comments.gmane.org/gmane.linux.uml.user/14270
http://rackerhacker.com/2007/08/24/apache-no-space-left-on-device-couldnt-create-accept-lock/
http://forum.directadmin.com/showthread.php?t=43938&page=1
http://blog.mohammadzadeh.info/index.php/apache-no-space-left-on
http://linuxwindowsmaster.com/fixing-apache-%E2%80%9Cno-space-left-on-device-couldn%E2%80%99t-create-accept-lock%E2%80%9D-errors/
(and many many others)

Even users suspected this's a bug and filed a bugzilla report:
https://issues.apache.org/bugzilla/show_bug.cgi?id=26265

Reading these posts, we can find that the problem confused even misled users to
check "disk space", "quota limit", etc.(the same as I), and "took me several
hours", "completely stumped", etc (also the same).

I strongly suggest to make the message more explicit and useful to users, and
let users check their semaphore limit directly. Most of users including me do
not know what does a mutex failure mean.

---------

The same thing applies to scoreboard creation failures. I used to get the error
message which takes me a lot of time to fix. The message is like:

[core:crit] [pid 15657:tid 140370438330112] (12)Cannot allocate memory:
AH00004: Unable to create or access scoreboard (anonymous shared memory
failure)

Similarly, I never configured scoreboard related stuff, and I don't know what a
scoreboard is and what is it used for.

(Searching on Internet, you can also find many users have the same problem!) 

It's not intuitive to users why setting a upper limit would cause shared memory
problem, if they do not understand the scoreboard mechanism used for IPC.

So, I suggest to tell users something like "Reduce the ServerLimit and
ThreadLimit settings, or clean the shared memory to increase the limit" in
addition to the scoreboard creation failure message. 

Thanks you very much!

Best regards,
Jackie Zhang

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