Market place studies has shown that Sun (Solaris) leads the commercial UNIX marketplace, followed by HP (HPUX). On the other hand, studies also show that Linux is the platform of choice for the vast majority of web servers.
You are correct and very bright in understanding that you must understand commerical flavors of UNIX to make the larger salaries and be more attractive to big commerical companies.
Getting a job with a large company really depends on the person you are inteviewing with, the geographic area, and the hiring culture. I have interviewed with companies that are more interested in overall UNIX experience than one particular one. I have interviewed with companies that are more interested in seeing how I memorized a command line switch relative to a single vendor implementation of a utility. BTW: I have never accepted a job with the latter. Great UNIX people don't memorize command switches, that is what the 'man pages' are for. Great UNIX people understand the system, not memorize it. There is a subtle difference which I will not bore you with in this thread (unless you ask).
In other words, there is not one right answer. This also depends on the level that you are working. If you are programming at the system call level using the C language, writing PERL, JAVA or PHP scripts, then the actual platform (SUN, HP, LINUX, et al) does not matter so much. Then again, the person interviewing you might not have enough experience to know that
If you are doing detailed system administration of super commerical systems such as HPUX or SOLARIS, then experience with the vendor unique implementations do make a big difference. However, a good basic understanding of the core principles of the UNIX/LINUX operating system are enough for most people. They can learn the job unique requirements.
The flexibility to learn on-the-job depends on the role. If you are a salaried employee, the learning, training is part of what the company is supposed to give you in return for paying you such a low salary On the other hand, if you are a highly paid consultant, then you will need to be able to 'hit the platforms' quickly and work without much learning curve. Or you should be talented enough with a broad exposure to 'get-up-to-speed fast'.
Since you are asking these questions about 'starting to learn UNIX' it is safe to assume that you are not going to be a 'highly paid consultant' tomorrow. That takes a few years of very solid expertise. If you are just starting, the odds are that you will be a salaried employee.
In the case of a salaried employee, who has learned UNIX/LINUX at home by working hard with the system calls as identified in thread:
You should have plenty of time to learn the specifics required on the job, depending the the job and your interest.
OBTW: You said you will 'learn UNIX, then LINUX'. Realistically, they are the same in principle. Don't let commercial 'trademark' issues confuse you in your quest for UNIX knowledge. UNIX is more of a 'way of computing and networking' vs. a product. Both LINUX, HPUX, SOLARIS, IRIX, AIX, etc all share the same basic 'way of computing and networking'. The differences are what make it interesting. Learning to be expert in this environment takes years, not a single training or series of two week certification courses.
In a nutshell, multitasking, distributed operating systems based on the UNIX design philosophy is a generic genre of knowledge. There is a vast amount of skills to learn depending on what your interests are. Most people change the exact nature of the work from project-to-project in order to gain more experience, keep themselves happy and challenged, and to build a solid resume so they can make better money and travel the world This process is not one that occurs overnight. It takes patience, hard work and discipline. Having a good solid college education in mathematics, computer science, or one of the major engineering disciplines is also a very big plus.
Personally, I have a degree in Electrical Engineering and had years of mathematical and engineering experience before learning UNIX. There is little doubt in my mind that this training was also very important in my career goals. I highly suggest every person who reads this thread continues with their college education, if they have not completed their higher education. There are a few good core OS UNIX books in addition to the Stevens books listed in thread 75.
BTW: My home library has at least 30 solid UNIX books as reference material. If you add books on JAVA, Apache, HTML, etc. the number goes up to 100 books quickly. I have found that the time and money spent reading and working examples in the books are much more rewarding than any combination of numerous $1200.00 training courses. If you have the discipline, studying the classic texts and working the code examples are the best course-of-action for becoming an expert. This approach, however, requires a passion for knowledge and is not for those seeking a 'shortcut'. I have not found any shortcuts in life that have been nearly as beneficial as just 'doing the work' step-by-step, inch-by-inch.
[Edited by Neo on 11-19-2000 at 09:12 AM]