If you get the following error with InnoDB in MySQL error log (var/log/mysql/error.log) :
InnoDB: Completed initialization of buffer pool
That means that InnoDB is not able to use the memory to work properly. And by consequent, it will quit MySQL with a fatal error, MySQL will crash and will stay down.
You will have to restart MySQL.
service mysql restart
You have then to create a Swap file to get more memory.
If it doesn’t work, you can also modify MySQL configuration file to allocate less memory to InnoDB work.
Add or modify (if the line already exists) :
innodb_buffer_pool_size = 20M
The default memory buffer pool is 128.0M.