In my current full-time role, I am a Linux System Administrator at a nonprofit institution. I came to this position from a mainly Windows environment, and wanted to refresh and solidify my Linux SysAdmin skillset. In order to do this, I chose the certification track so that I could re-cover all the basics before learning specialized skills for this particular organization.
I started out with the basic Linux+ certification by reading the Sybex CompTIA Linux+ book as well as starting a subscription to Linux Academy. This online site includes a ton of video instruction as well as VMs so that you can practice all your skills and tasks without having to have your own local Virtualbox or other server environment. This VM addition really removes a lot of the pain and overhead while learning and studying for your certs. I think the cost is ~$20 / month and I highly recommend this service.
Next, I obtained Redhat’s RHCSA certification. Though my office sent me to the ‘official’ 1-week training, and that was useful, I feel that both practice IRL as well as the Linux Academy stuff would have been enough to pass the exam.
Currently working on RHCE. Hopefully will get this done over the next couple of months. Though no certification an substitute for practical experience, and no training takes the place of years of troubleshooting and break / fix experience, I still feel that certification is useful.