Upgrading Ubuntu from 15.04 to 16.04

There are few issues after the upgrade:

SSH

If you were using ssh key with DSA (dss keytype), you need to enable dss keytype in your sshd_config file (the following config). See this page for more details.

PubkeyAcceptedKeyTypes=+ssh-dss

If your client is OpenSSH 7.0, you will have to add the config above to your ssh_config file as well.

MySQL

If you were using Mysql 5.5 or 5.6, you need to update your mysql configuration file because there are some config deprecation. Here are the work arounds: https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1571865

Of course you can grep and rename the config manually.

PHP

Please note that once you upgraded your Ubuntu Linux to 16.04, the previous installed PHP will be upgraded to PHP7 and you can’t go back.

If you want to go back to PHP5, you have to use Ubuntu PPA to get the older PHP versions. (Or you can use phpbrew to build multiple phps)

The FPM sock path is also changed. Remember to replace your fastcgi socket path with the following line:

/var/run/php/php7.0-fpm.sock

If you’re using doctrine annotation parse based tools, remember to enable opcache.load_comments config, or you will see the following error message:

You have to enable opcache.load_comments=1 or zend_optimizerplus.load_comments=1

Finally

Remember to backup all data before running “do-release-upgrade”