Could you further clarify what, to you, means "to learn Linux"?
I ask, because, like SQL, learning to use SQL, for querying, isn't always as inclusive as learning how to "structure" (or normalize, if term still used) data to be stored in an SQL database, or further, what indices some SQL tables/relations should have and/or how SQL tables/relations should be "mapped" on server disk drives (to maximize) performance. I.e. there's a range of skills differences, possibly between being a SQL expert user and an SQL DBA expert - one person might have the whole range covered, part of the range, or various levels of expertise across the range.
Likewise, Linux expertise encompasses quite a range too.
Since this is a networking community, and you mention studying for CCNP, you might actually never need to know much about using Linux yet to be a true "networking" expert, you might need to keep abreast of the features/options of Linux networking stacks, especially as some of the most "bleeding edge" network stacks can be obtained for Linux platforms (which, might be used on user hosts and/or server hosts). I.e. you might need to be able to recommend try this networking stack, with these options and/or DON'T use that networking stack.
Again, if you want to break into the networking industry, knowing just the basics of using Linux, would normally be considered a plus, or even possibly a job requirement, but unless your job requires you to build a network management station, on a Linux platform, from a bare bones system, often you don't need to know much about Linux (besides, possibly, the impact of different network drivers).
BTW, the forgoing is assuming you're a full time network engineer, not a part time network engineer and systems/server administrator. If the latter, you would likely need to know much more about Linux.
