MySQL: Unknown table engine ‘InnoDB’

mysql> show innodb status
Unknown table engine ‘InnoDB’

I got this message when tried to allocate a huge size of memory on remote server,
innodb_buffer_pool_size = 8000M

after i have looked for memory:
free -m
and have found that there are only 4gb,

change option to:
innodb_buffer_pool_size = 2000M

and mysql has been start fine with innodb.