Thank you for the response.
You were right, mysql doesn’t stoped correctly.
Now I use the command service mysql stop and it works fine.
Can I ask you a second question ?
I’ll setup an incremental backuping to save bandwith. I made no changes on the databases and i’ve made an incremental backup, the size of the folder is the half of the full backup ( full = 660Mo, incremental with no changes = 300Mo). Is there an option for getting only the diff in incremental.