Db2_install do not have write permission on the directory or file

This is the error I encountered (I ran the db2_install and everything else as root,):

DBI1288E  The execution of the program /home/DB_SERVER/ibm/db2/v10.5 failed. This
      program failed because you do not have write permission on the
      directory or file .

I tried to change the access permission of the path:

chmod -R a+rw /home/DB_SERVER/ibm/db2/v10.5

And then I could create a new file in that folder:

vi test

Result of ll in that directory:

total 1
-rw-rw-rw- 1 root root 12 Nov 23 00:24 test

But when I ran the db2_install again, it failed for the same reason.

PS: I tried to change permission of the setup file too

chmod -R a+rwx db2Setup/

Result of ll

total 72
drwxrwxrwx  6 root root 4096 Nov 23 00:10 db2
-rwxrwxrwx  1 root root 5349 Nov 23 00:10 db2ckupgrade
-rwxrwxrwx  1 root root 5302 Nov 23 00:10 db2_deinstall
-rwxrwxrwx  1 root root 5172 Nov 23 00:10 db2_install
-rwxrwxrwx  1 root root 5136 Nov 23 00:10 db2ls
-rwxrwxrwx  1 root root 5154 Nov 23 00:10 db2prereqcheck
-rwxrwxrwx  1 root root 5154 Nov 23 00:10 db2setup
drwxrwxrwx 10 root root 4096 Nov 23 00:10 ibm_im
-rwxrwxrwx  1 root root 5190 Nov 23 00:10 installFixPack
drwxrwxrwx  4 root root 4096 Nov 23 00:10 nlpack
-rw-r--r--  1 root root    8 Nov 23 01:00 test

So I have no idea what's wrong? How to fix this?