Hi abelleba,
Some 60 people read your post and not even one remark. Well, I can not really call myself a Linux professional, cause I never made and money with Linux. Anyway, if you want certification to push your job getting skills you need to take a very broad approach.
You might be in a city that has a local college hat can give you some help with getting papers that impress employers. The object is not to get better skills, but to show that you can pass tests to show you know how to study. Even a subject that you think is a dead end. Some have on-line courses that get you credits that will look good on your resume. You will not find this advertised on the internet. You have to go to the campus and find out what they have. There are programs they have to reduce the fees is you have some reason. Like maybe you have a family to support.