Linux commands are instructions that are issued on the command line when working under a Linux operating system known as a distribution, "distro" or "flavor." Commands can be thought of as orders given to the operating system or to a software program running under the system to make it do something or to force it to quit doing something, such as running a process. It can be said that Linux commands are a kind of language via which a person can communicate with software and even control hardware.
Letters, numbers and symbols are used in different combinations to form Linux commands that can accomplish tasks such as changing run levels or creating, deleting, modifying and copying files and directories. Linux commands are used to create and manage users on a multi-user system, add and manage local and network printers, control network interfaces, set the date and time and reboot or shut down a system. Working on the Linux command line does not involve the use of a mouse, as is usually the case when working within a graphical user interface (GUI). There are usually only two colors seen — the color of the background and the color of the text — and there is no room for mistakes, which can be devastating to a system if the user is working as the root operator.
Unlike accidentally clicking on an icon in most cases, making a mistake when issuing Linux commands can result in error messages or undesired surprises. Error messages can occur when a mistake is made that the system does not understand. While an accidental click on an icon will still open the program, if all is working properly, a mistake in the syntax of Linux commands might not be understood. For example, the command "cd," which allows the operator to change directories, will not be understood if it is mistyped as "cf." The command "rm -f," which is used to force a deletion or the removal of a file, if typed by mistake, can result in the loss of data.
Many commands are the same as or are similar to Unix commands, because all distributions of Linux are Unix-based systems. For example, the command "ls" lists all of the files in the current directory, and "pwd" prints the working directory on a Linux and Unix system. Commands must not only be spelled correctly, they must be in the correct case, because Linux is a case-sensitive system. There are many commands that have to be used to manage a system completely without using a GUI. Not only must the commands be learned, the arguments that can and sometimes must be passed to them need to be learned, along with knowing how to request a help menu from within the system.
The reason why it is important to work with Linux commands even when running a distribution with an advanced windows system is because certain administrative tasks cannot be performed efficiently or at all except on the command line. Basic Linux commands can be learned from tutorials that are available free of charge on the Internet and from books on the subject. These orders actually command the system, so it is very important for users to review what orders are being issued before pressing enter. A root user has full control of the system. Issuing commands that are not fully understood or that are misused can destroy the integrity of an entire system.
