I’ve copied my
/var/www, MySQL database, and
/etc from a sever to an other server.
After this I found that my MySQL does not work anymore.
The reason for the trouble was that
/etc/mysql/debian.cnf contains (twice) an auto-generated password for the database, and so after copying my old
/etc directory from my old server the password didn’t match the new password stored in my MySQL database.
The solution: Do not overwrite
/etc/mysql/debian.cnf file when copying
/etc directory, but leave it as it was autogenerated by the new server installation script.
Note: This is a about Debian Linux.