I tried a lot to install mailinabox on linode ununtu 14.0 server but can't

When installing Mail-in-a-Box on Ubuntu, make sure you're doing so on a Linode with an Ubuntu 18.04 distribution as its operating system, because with the latest version of MIAB (starting with version 0.40),only Ubuntu 18.04 is supported.

My recommendation is to create a new Linode (it'll be quicker than upgrading your current distribution) and following the guide we've put together on Mail-in-a-Box:

How to Create an Email Server with Mail-in-a-Box

Thanks a looooooot , I tried to solve the problem for more than 2 days but can't.

Finally solved it after your advice.
so thank you a lot again.