I am facing problem restoring a MySQL database. My primary database was MySQL 5.1 and now I am trying to copy it to MySQL 5.5. The database was backed up by using Xtrabackup.

I am using Ubuntu 12.04.3 LTS on this server, MySQL version is: `5.5.32-0ubuntu0.12.04.1-log`.

I have followed all the steps to restore using Xtrabackup, this created database files, which I have copied to a tmp directory.

I have modified `my.cnf` to point to this tmp directory. I have changed the tmp directory permissions and changed the ownership of the files to `mysql` user. 

 drwxr-xr-x 12 mysql mysql 4096 Sep 10 10:04 base

Now when I start the MySQL server I get this error:

> [ERROR] Fatal error: Can't open and lock privilege tables: Table 'host' is read only

I have given a try as follows:

 1. Even tried installing MySQL 5.1 to see if that was the issue.
 2. tried `chcon mysql_db_t` to change the context but it gives me:

 > can't apply partial context to unlabelled file

 3. I have used `--skip-grant` to get into database, but using this I can only access InnoDB tables only, MyISAM tables throw read-only error.
 4. After `--skip-grant`, I have used `upgrade_mysql`. This throws me errors stating that many tables are read-only.
 5. I have removed AppArmor too. And restarted too.
 6. I have restored a different database (5.1 to 5.5) previously on Ubuntu 12.04.2 LTS without any issues.

Can some please point me in right direction? I am not sure whats wrong with permissions.