5.1.4 Basic commands of operating system

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According to the already mentioned, a user who has an account you can login to the system. If you use the console or terminal-emulator for system administration offered work through the shell - COMMAND INTERPRETER, by default shell is BASH, allows command task to the system. General command is the process that is to be executed and that the execution of orders received over the input and gives a result in one of the exits, according to the following picture.

 Linux Process 0 - standard input (stdin)

1 - standard output (stdout)

2 - standard error (stderr)
Figure 5.1.9 The process and its basic input / output characteristics.

The usual standard input is the keyboard, or the keyword listed options and arguments. With pressing <Enter> shell allows the process to take the order, comply with his treatment and if all went as expected result of the process passes to standard output, and if not forward it to the standard error. Based on such understanding process activity leads to the conclusion that one of the outputs can be input into another process and exit from it in the next entry - CHAINING.

Either way, there are a lot of commands, more or less complex and with more or less options. All this has a lot and so it is constantly consulted help pages or literature. The execution of a command is a process, that when it comes to red for thors doing their share, is expected to accept data input (stdin) - read operation from either the keyboard or the contents of a file or the output from another process, and as a result has properly processed data at the output (stdout) - write operations, or an error message if the treatment failed or interrupted (stderr) - error messages. All activities of the process are recorded in the corresponding files to monitor his work, so LOG file in the [/var/log] directory.

During operation, the user has a need to 'cleanse' display to clearly read the result of the next command. The command ' clear ' serves for this purpose. Commands that were previously shown, as well as contents of a directory in which they are located, are the most fundamental part of the operating system, resulting in installing the operating system over the network without requiring any additional program support that is shown in Figure 5.5c.

All commands are available to users. If you want to execute some special actions, particularly changes in the configuration file directory [/etc] or upgrade the system itself, a user must have the authority of supervisors, which is identified by the username ' root '. Apart from the console, there is no other way to directly use the username ' root '. The powers of a system administrator can be achieved through the terminal command ' su ' as follows:

    drago@voda:~$       (users 'drago' positioned in its working directory)
    drago@voda:~$ su -  (command to obtain the status SUPERVISOR (root); following query type the
                         password for the 'root' user with the transfer of environment variables)
    voda:~#             (working directory of the user 'root')
    voda:~# cd /
    voda:/#             (root directory of the system)

Administrator privileges may be restricted only to the target group of users, so if the system is to be used under strict supervision, provides the root user only from the console. Way of getting the root authority is shown in Figure 5.1.2a. In addition there is a brief description of the main commands of the system, which are located in directories [/bin], [/sbin] and [/usr/bin]. For efficient use of commands before that should always read the instructions that describe them in detail, particularly with regard to a multitude of options. The basic syntax of the command is described in specific terms of IT, Chapter 5.1.1.

Fundamental commands

A number of them in the examples so far used include, but here most of the controls and relevant Key Words (KW). Further shows commands to read instructions for key words and basic file system commands.

Manage file system

Linux file system is based on a unique original location (the root), which is simply denoted with a ' / ', which are connected to all the files and directories associated with their directories and files and so further to FSSTND hierarchical structure. The basic feature of this concept is that for any directory in the structure can 'hook' the new structure set up by the same principle. Commands for working with the file system are:


Commands that follow refer to the file, whether it is related to the physical device, the executable (binary) and directories, as well as text files. The commands used for its retrieval and browsing. The purpose is to obtain usable although in view of their misuse can in the worst case, make that everything on the screen illegible.

Display control

When the display during operation shows 'junk', or by pressing the arrow button to receive some unimportant character, one may serve to save the commands in this chapter.

Compressed files

In order to save space on your hard drive, a lot of files that are used are compressed. Programmes such as 'gzip' or 'compress' substantially reduce their size, often more than three times. In the era of disks with large capacity stated it more relevant, but it was as a rule. Compressed files can not be read directly, but first be unzipped. Some software support, as well as the ' GNU Midnight Commander ' - ' mc ', has an integrated mechanism for extracting the file to a temporary file in the directory [/tmp] and read its contents.


Regular backups are required, especially if the server is standalone and does not replicate with another in a network, in order to be able to recover the system and data in case of disaster. To get full access to all the files you need to archive, a full backup must be performed by a superuser. Subsequent programs (commands) are used for making backups of different types:

Control over events

The events are a series of events between applications on your computer system and check-out from your computer system. Be aware that by signing up to the user to gain administrative rights, can do great harm to the system just plain wrong typing commands. Especially if no command has recursive properties.

Users and computer

Commands that relate to the user's identity and the identity of the computer are:

Described controls are not all that are in directories [/bin], [/sbin] and [/usr/bin], but are the most important for successful host configuration, monitoring its operation and resolving business problems. In addition is shown only the basic part, without the many other options that can be joined to each command.


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