Mysql Can't create/write to file error#13

Question

I had created a Django view which is returning some data after reading from MySql DB.When i try and fetch around 6000 rows from the Database,everything works fine and the view returns HttpResponse as is expected.However as i try to fetch 7000+ rows i get the following error

(1, "Can't create/write to file '/home/nipun/mysql_temp/MYzplJok' (Errcode: 13)")

Earlier i thought that the error could be due to space getting exhausted for /temp,so i changed the tempdir setting in my.cnf
I also ensured that new tmpdir /home/nipun/mysql_temp and it's parent directories are writable by me by changing the ownership. Although this is not a Django problem,here is the view

def query_json(request):
    from django.utils import simplejson
    objects=Publisher.objects.filter(location='ROOM_01',sensor_name='CPU_TEMPERATURE').order_by('-id')[0:9000]

    json = simplejson.dumps( [{"reading": float(o.reading),
                           "timestamp": str(o.timestamp)
                       } for o in objects] )

    return HttpResponse(json,mimetype="application/json")

So in the filter changing 9000 to 6000 works fine.
Some more information about the error is provided in the Django stack trace

errorclass  
<class '_mysql_exceptions.InternalError'>
errorvalue  
InternalError(1, "Can't create/write to file '/home/nipun/mysql_temp/MYuotga9' (Errcode:     13)")
error   
(<class '_mysql_exceptions.InternalError'>,
InternalError(1, "Can't create/write to file '/home/nipun/mysql_temp/MYuotga9' (Errcode: 13)"))

EDIT
As per a comment, i tried this on my MySQL prompt

mysql> CREATE TEMPORARY TABLE t (i int);
ERROR 1005 (HY000): Can't create table 't' (errno: 13)

So it essentially is now an issue of how to allow MySQL to write to temporary directory

Answer 1

It is probably a permission issue for the temporary folder that is used by Mysql.

You can find the folder used by Mysql for temp operations in the config file in /etc/mysql/my.cnf as such :

tmpdir          = /tmp

As you can see, the temp folder in use by default is "/tmp".

Privileges should be :

drwxrwxrwt   9 root root  4096 oct.  24 15:39 tmp/

So anybody, including the "mysql" user, can use it. If not correctly set, the following command would do the trick :

chmod 0777 /tmp

Hope this helps !