Multiuser — We have many user accounts available on a Linux system, you can also have multiple users logged in and working on the system at the same time. Users can have their own environments arranged the way they want: their own home directory for storing files and their own desktop interface (with icons, menus, and applications arranged to suit them). User accounts can be password-protected, so that users can control who has access to their applications and data.
Multitasking — In Linux, it is possible to have many programs running at the same time, which means that means not only we have many programs running, but the Linux operating system can itself have programs running in the background. Many of these system processes make it possible for Linux to work as a server, with these background processes listening to the network for requests to log in to your system, view a Web page, print a document, or copy a file. These background processes are referred to as daemons.
Graphical User Interface — The powerful framework for working with graphical applications in Linux is referred to as the X Window System (or simply X). X handles the functions of opening X-based graphical user interface (GUI) applications and displaying them on an X server process (the process that manages your screen, mouse, and keyboard).
Multitasking — In Linux, it is possible to have many programs running at the same time, which means that means not only we have many programs running, but the Linux operating system can itself have programs running in the background. Many of these system processes make it possible for Linux to work as a server, with these background processes listening to the network for requests to log in to your system, view a Web page, print a document, or copy a file. These background processes are referred to as daemons.
Graphical User Interface — The powerful framework for working with graphical applications in Linux is referred to as the X Window System (or simply X). X handles the functions of opening X-based graphical user interface (GUI) applications and displaying them on an X server process (the process that manages your screen, mouse, and keyboard).
On top of X, you use an X-based desktop environment to provide a desktop metaphor and window manager to provide the look-and-feel of your GUI (icons, window frames, menus, and colors, or a combination of those items called themes). There are several desktop environments and several desktop managers to choose from. (Red Hat provides a few desktop managers, but focuses on GNOME and KDE desktop environments.)
Hardware support — You can configure support for almost every type of hardware that can be connected to a computer. There is support for floppy disk drives, CD-ROMs, removable disks (such as DVDs and Zip drives), sound cards, tape devices, video cards, and most anything else you can think of. 
| Command | Meaning |
|---|---|
| > | Redirect output |
| >> | Append to file |
| < | Redirect input |
| << | "Here" document (redirect input) |
| | | Pipe output |
| & | Run process in background. |
| ; | Separate commands on same line |
| * | Match any character(s) in filename |
| ? | Match single character in filename |
| [ ] | Match any characters enclosed |
| ( ) | Execute in subshell |
| ` ` | Substitute output of enclosed command |
| " " | Partial quote (allows variable and command expansion) |
| ' ' | Full quote (no expansion) |
| \ | Quote following character |
| $var | Use value for variable |
| $$ | Process id |
| $0 | Command name |
| $n | nth argument (n from 0 to 9) |
| $* | All arguments as a simple word |
| # | Begin comment |
| bg | Background execution |
| break | Break from loop statements |
| cd | Change directories |
| continue | Resume a program loop |
| echo | Display output |
| eval | Evaluate arguments |
| exec | Execute a new shell |
| fg | Foreground execution |
| jobs | Show active jobs |
| kill | Terminate running jobs |
| newgrp | Change to a new group |
| shift | Shift positional parameters |
| stop | Suspend a background job |
| suspend | Suspend a foreground job |
| time | Time a command |
| umask | Set or list file permissions |
| unset | Erase variable or function definitions |
| wait | Wait for a background job to finish |
