My job description does not include the phrase "system administration", but I most certainly perform those duties on a regular basis. At least I enjoy it!
Over the years, I've accumulated a fair amount of knowledge about Linux; especially CentOS, which I use at home, and Red Hat Enterprise at work (where I've also been dealing with AIX fairly regularly, and even Solaris and HP-UX on rare occasion).
Q&A for system and network administrators
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Q&A for enthusiasts and power users of the Android operating system