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From Nan Ge <genan...@gmail.com>
Subject Re: mod_jk failed to map shared memory with errno=5
Date Thu, 20 Nov 2014 03:25:07 GMT
On Thu, Nov 20, 2014 at 8:54 AM, Konstantin Kolinko <knst.kolinko@gmail.com>
wrote:

> 2014-11-19 12:47 GMT+03:00 Nan Ge <genan.zh@gmail.com>:
> > I'm using Apache-httpd-2.4.10(Win64) and apache-tomcat-8.0.12-windows-x64
> > with tomcat-connectors-1.2.40-windows-x86_64-httpd-2.4.x (mod_jk) on
> > windows8.1x64 for load balancing, my configuration about mod_jk in
> > httpd.conf:
> >
> > LoadModule    jk_module  modules/mod_jk.so
> > JkWorkersFile conf/workers.properties
> > JkLogLevel    info
> > JkLogStampFormat "[%a %b %d %H:%M:%S %Y] "
> > JkLogFile     logs/httpd/mod_jk.log
> > JkShmFile     logs/mod_jk.shm
> > JkMount  /myapp/* lb
> >  <Location /jkmanager/>
> >     JkMount jkstatus
> >     Order deny,allow
> >     Deny from all
> >     Allow from 127.0.0.1
> >  </Location>
> >
> > and here is my workers.properties:
> > worker.list= lb,jkstatus
> > worker.jkstatus.type=status
> > worker.lb.type=lb
> > worker.lb.balance_workers=tm1,tm2
> > worker.tm.type=ajp13
> > worker.tm.host=127.0.0.1
> > worker.tm.lbfactor=1
> > worker.tm1.reference=worker.tm
> > worker.tm2.reference=worker.tm
> > worker.tm1.port=8009
> > worker.tm2.port=8010
> >
> > After apache was started, I cannot open the /jkmanager page, I checked
> the
> > logs/ directory and no mod_jk.shm file was found, and I checked
> > mod_jk.log with following error :
> >
> > [Wed Nov 19 15:40:20 2014] [4296:8648] [info] init_jk::mod_jk.c (3383):
> > mod_jk/1.2.40 initialized
> > [Wed Nov 19 15:40:20 2014] [4296:8648] [error] jk_shm_open::jk_shm.c
> (240):
> > Failed to map shared memory
> > F:/server/httpd-2.4.10-x64-vc11/Apache24/logs/mod_jk.shm with errno=5
> > [Wed Nov 19 15:40:20 2014] [4296:8648] [error] init_jk::mod_jk.c (3366):
> > Initializing shm:(null) errno=5. Load balancing workers will not function
> > properly.
> > ...
> >
> > It seems that mod_jk could not create mod_jk.shm file
>
> Looking at the source code:
>
> 1) The doc [1] say that JkShmFile option is "Used only on unix platforms."
>
> The actual code is that
> a) On unix platforms it is used always, as documented.
>
> If no JkShmFile is specified then a warning is printed and the default
> name "logs/jk-runtime-status" is used.
>
> b) On Windows this feature can be used.
> It is disabled by default and used only if JkShmFile is set explicitly.
>
> Question 1: Do you need JkShmFile at all.
>
> Fixme: If you (or anyone else) succeed in using JkShmFile on Windows
> then I think the doc shall be updated to mention the use on Windows.
>
> On Windows:
> If JkShmFile is not set then it results in allocating some block of
> memory without any special properties.
>
> If JkShmFile is set then it does the work with mapped files
> (CreateFileMapping and other Win API methods)
>
>
> 2) The CreateFileMapping method that is used to initialize memory
> mapping is called in jk_shm.c as
>
>             jk_shm_map = CreateFileMapping(INVALID_HANDLE_VALUE,
>                                            jk_get_sa_with_null_dacl(),
>                                            PAGE_READWRITE,
>                                            0,
>                                            (DWORD)shmsz,
>                                            shname);
>
> See [2] for documentation. Note that
> - hFile is INVALID_HANDLE_VALUE
> - shname is "Global/" + some string created from filename.
> - shmsz is the size that you specified in configuration as JkShmSize.
> By default it is calculated automatically, it is usually recommended
> to allow it to be calculated automatically.
>
> It means that:
> a) That value of hFile means that there is no "mod_jk.shm" file here.
> The mapping is allocated from the system page file.
>
> Question 2: Do you have system page file enabled? (I think that some
> systems may have it disabled).
>
>
> It it is not a file, then you can simplify your configuration: Remove
> the "logs/" prefix from the name.
>
> 3) There may also be some Windows-specific issues, like security
> restrictions etc. Some are mentioned in [2].
>
> Is "jk_get_sa_with_null_dacl()" used in CreateFileMapping() call a
> correct value?
>
> GetLastError() returning 5 means ERROR_ACCESS_DENIED - from [3].
>
>
>
> Fixme: Can the error message be improved? There is no actual file
> here, but it mentions a file name. It is a bit misleading (as one
> thinks that it tires to access a file), but it is good as it mentions
> the value that actually exists in configuration.
> It also does not mention how many bytes it tried to allocate.
> It can be something like "Failed to allocate xxx bytes for shared
> memory named yyy.  GetLastError returned zzz".
>
> [1] http://tomcat.apache.org/connectors-doc/reference/apache.html
>
> [2] MSDN - CreateFileMapping function
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/aa366537%28v=vs.85%29.aspx
>
> [3] MSDN - System Error Codes
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms681381%28v=vs.85%29.aspx
>
>
> Best regards,
> Konstantin Kolinko
>
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>
Thanks Kolinko!

It has been resolved by Running httpd.exe as Administrator, as you had
mentioned that it has something to do with system security restrictions.
Now the mod_jk.log shows: "[info] init_jk::mod_jk.c (3383): mod_jk/1.2.40
initialized", and I can access /jkmanager page successfully.
I checked the logs/ directory again, 'mod_jk.shm' is still not found, as
you said it might have been allocated from the system page file.
Thanks for your help!

Best regards,
Nan Ge

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