Linux Filesystem Hierarchy

kernel
Part of an operating system that implements the interaction with hardware and the sharing of
resources.
libraries
Executables should have no undefined symbols, only useful symbols; all useful programs refer to
symbols they do not define (eg. printf or write). These references are resolved by pulling object files
from libraries into the executable.
link
A symbolic link (alias in MacOS and shortcut under Windows) is a file that points to another file; this
is a commonly used tool. A hard−link rarely created by the user, is a filename that points to a block of
Linux Filesystem Hierarchy
Glossary
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data that has several other filenames as well.
man page
Every version of UNIX comes with an extensive collection of online help pages called man pages
(short for manual pages). The man pages are the authoritative documentation about your UNIX
system. They contain complete information about both the kernel and all the utilities.
MTA
Mail Transfer Agents. Alongside the web, mail is the top reason for the popularity of the Internet.
E−mail is an inexpensive and fast method of time−shifted messaging which, much like the Web, is
actually based around sending and receiving plain text files. The protocol used is called the Simple
Mail Transfer Protocol (SMTP). The server programs that implement SMTP to move mail from one
server to another are called MTAs. Once upon a time users would have to Telnet into an SMTP server
and use a command line mail program like 'mutt' or 'pine' to check their mail. Now, GUI based e−mail
clients like Mozilla, Kmail and Outlook allow users to check their email off of a local SMTP sever.
Additional protocols like POP3 and IMAP4 are used between the SMTP server and desktop mail
client to allow clients to manipulate files on, and download from, their local mail server. The
programs that implement POP3 and IMAP4 are called Mail Delivery Agents (MDAs). They are
generally separate from MTAs.
NFS
Network File System, is the UNIX equivalent of Server Message Block (SMB). It is a way through
which different machines can import and export local files between each other. Like SMB though,
NFS sends information including user passwords unencrypted, so it's best to limit its usage to within
your local network.