Linux

A reason for FATAL → Failed to fork error usually occurs when memory has been exhausted.

As seen on the command line

Setting up mysql-client-5.5 (5.5.32-0ubuntu0.12.04.1) ...
Setting up mysql-server-core-5.5 (5.5.32-0ubuntu0.12.04.1) ...
Setting up mysql-server-5.5 (5.5.32-0ubuntu0.12.04.1) ...
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
mysql start/running, process 7867
Setting up libhtml-template-perl (2.10-1) ...
Setting up libmysqlclient-dev (5.5.32-0ubuntu0.12.04.1) ...
Setting up mysql-client (5.5.32-0ubuntu0.12.04.1) ...
Setting up mysql-server (5.5.32-0ubuntu0.12.04.1) ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
FATAL -> Failed to fork.

A seen on SolusVM Memory Usage

memory_usage.png

Quick Fix

A quick fix would be to reboot your system. Memory is then released so you will have free memory available for the next tasks.

Long Term Fix

A long term fix for this is to increase your memory.