For example, add user jerry to groups ftp, www_data:

useradd -G ftp,www_data jerry

• / : root directory
• ./ : current directory
• ./command_name : run a command in the current directory when the current directory is not on the path
• ../ : parent directory
• ~ : home directory
• $ : typical prompt when logged in as ordinary user
• # : typical prompt when logged in as root or superuser
• ! : repeat specified command
• !! : repeat previous command
• ^^ : repeat previous command with substitution
• & : run a program in background mode
• Tab][Tab] : prints a list of all available commands. This is just an example of autocomplete with no restriction on the first letter.
• x[Tab][Tab] : prints a list of all available completions for a command, where the beginning is ``x''
• [Alt][Ctrl][F1] : switch to the first virtual text console
• [Alt][Ctrl][Fn] : switch to the nth virtual text console. Typically, there are six on a Linux PC system.
• [Alt][Ctrl][F7] : switch to the first GUI console, if there is one running. If the graphical console freezes, one can switch to a nongraphical console, kill the process that is giving problems, and switch back to the graphical console using this shortcut.
• [ArrowUp] : scroll through the command history (in bash)
• [Shift][PageUp] : scroll terminal output up. This also works at the login prompt, so you can scroll through your boot messages.
• [Shift][PageDown] : scroll terminal output down
• [Ctrl][Alt][+] : switch to next X server resolution (if the server is set up for more than one resolution)
• [Ctrl][Alt][: ] : change to previous X server resolution
• [Ctrl][Alt][BkSpc] : kill the current X server. Used when normal exit is not possible.
• [Ctrl][Alt][Del] : shut down the system and reboot
• [Ctrl]c : kill the current process
• [Ctrl]d : logout from the current terminal
• [Ctrl]s : stop transfer to current terminal
• [Ctrl]q : resume transfer to current terminal. This should be tried if the terminal stops responding.
• [Ctrl]z : send current process to the background
• reset : restore a terminal to its default settings
• [Leftmousebutton] : Hold down left mouse button and drag to highlight text. Releasing the button copies the region to the text buffer under X and (if gpm is installed) in console mode.
• [Middlemousebutton] : Copies text from the text buffer and inserts it at the cursor location. With a two: button mouse, click on both buttons simultaneously. It is necessary for three: button emulation to be enabled, either under gpm or in XF86Config.

• .bash_logout - file executed by bash shell on logout
• .bash_profile - initialization of bash shell run only on login. Bash looks first for a .bash_profile file when started as a login shell or with the -login option. If it does not find .bash_profile, it looks for .bash_login. If it doesn't find that, it looks for .profile. System-wide functions and aliases go in /etc/bashrc and default environment variables go in /etc/profile.
• .bashrc - initialization command run when bash shell starts up as a non-login shell
• .cshrc - initialization commands that are run automatically (like autoexec.bat) when C shell is initiated
• .emacs - configuration file for emacs editor
• .fvwmrc - configuration file for fvwm window manager
• .fvwm2rc - configuration file for fvwm2 window manager
• .jedrc - configuration file for the jed text editor
• .lessrc - typically contains key bindings for cursor movement with the less command
• .login - initialization file when user logs in
• .logout - commands run when user logs out
• .wm_style - gives choice of default window manager if one is not specified in startx
• .Xdefaults - sets up X resources for individual user. The behavior of many different application programs can be changed by modifying this file.
• .xinitrc - initialization file when running startx. Can be used to activate applications, run a given window manager, and modify the appearance of the root window.
• .xsession - configuration file for xdm