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I am trying to move the data directory of my MySQL database to a second disk array that I have as a mount point /array2/.

The problem I am having is I have tried everything and after I modify the location of datadir in my.cnf mysql will not start up again.

All I get is:

start: Job failed to start
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4 Answers 4

up vote 28 down vote accepted

Forgot about app armour.

For anyone that is interested I did the following to move the folder.

Stop the mysql server:

stop mysql

Create the new directory:

mkdir /array2/mysql

Copy over ONLY the database folders:

cp -R /var/lib/mysql/mysql /array2/mysql
cp -R /var/lib/mysql/users /array2/mysql

Backup the my.cnf file:

cp /etc/mysql/my.cnf /root/my.cnf.backup

Edit the my.cnf file:

nano /etc/mysql/my.cnf

Change all mentions of the old datadir and socket to your new location

Mine became:

datadir=/array2/mysql
socket=/array2/mysql/mysql.sock

Update the directory permissions:

chown -R mysql:mysql /array2/mysql

Rename the old directory:

mv /var/lib/mysql /var/lib/mysql-old

Create a symlink, just in case:

ln -s /array2/mysql /var/lib/mysql 

Let AppArmor know about the new datadir:

echo "alias /var/lib/mysql/ -> /your/new/datadir/," >> /etc/apparmor.d/tunables/alias

Reload the apparmor profiles

sudo /etc/init.d/apparmor reload

Then start mysql:

start mysql
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This is a good answer but you may need one more step to allow clients to connect to mysql. Add a new group with one line under it... [clients] socket=/array2/mysql/mysql.sock where the socket= portion points to the new location of your mysql.sock file. –  Night Owl Jan 30 '13 at 5:20
    
If you don't want to be bothered to merge /etc/apparmor.d/usr.sbin.mysqld each time mysql receives an update, you can add /array2/mysql/** rwk, to /etc/apparmor.d/local/usr.sbin.mysqld instead. Mysql will still have access to the old data dir, but that probably isn't an issue. –  drevicko Jul 26 '13 at 3:46
    
sed -i "s,datadir.*=.*,datadir=$new_dir,g" /etc/mysql/my.cnf. Why only the database folders? –  int_ua Apr 26 at 16:36
    
For anyone moving their datadir to ZFS (like I did), make sure you also add: innodb_use_native_aio=0 in the [mysqld] section of your my.cnf file, since ZFS on linux does not support AIO. dev.mysql.com/doc/refman/5.5/en/… –  Andrew Oct 3 at 20:04

I found that AppArmor was the culprit by examining the syslog, and was able to successfully change the mysql data location by following this process.

Please note that, in files edited below, lines starting with + were added, and lines starting with - were removed. You should not actually type/paste the + signs when adding lines to these files.

I cloned the mysql directory to the new location:

sudo rsync -av /var/lib/mysql /new_dir

Then I edited the datadir line in /etc/mysql/my.cnf:

sudo vi /etc/mysql/my.cnf
-datadir     = /var/lib/mysql
+datadir     = /new_dir/mysql

Then I edited /etc/apparmor.d/usr.sbin.mysqld:

sudo vi /etc/apparmor.d/usr.sbin.mysqld
-  /var/lib/mysql/ r,
-  /var/lib/mysql/** rwk,
+  /new_dir/mysql/ r,
+  /new_dir/mysql/** rwk,

Then I restarted mysql.

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Be aware.

If you have InnoDB tables you MUST copy over the ibdata* and ib_logfile* files or you will not be able to use the the tables. You will get:

'Table 'databaseName.tableName' doesn't exist'

errors.

Run this copy command to copy over the ibdata* and ib_logfile* files.

sudo cp -p /var/lib/mysql/ib* /array2/mysql/
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If you move your datadir, you not only need to give the new datadir permissions, but you need to insure all parent directories have permission.

I moved my datadir to a hard drive, mounted in Ubuntu as:

/media/*user*/Data/

and my datadir was Databases.

I had to set permissions to 771 to each of the media, user and Data directories:

sudo chmod 771 *DIR*

If this does not work, another way you can get mysql to work is to change user in /etc/mysql/my.cnf to root; though there are no doubt some issues with doing that from a security perspective.

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