Overview of Linux

Linux File system Hierarchy

What are file systems?
- Data structure and behavior that an operating system implements to keep track of files on a disk or partition to organize of files and directories [1].
- Before a disk can be used, it should be formatted with certain file system, which initialized data structures need to be written to the disk.
- Unlike Windows file system (NTFS/FAT), there is only one root in the file system hierarchy of many Unix clones i.e. /, known as root.
- Unlike in Windows, Unix system don’t have the concept of Drives (e.g. C: or D:), so each partition in physical hard disk should be associated or linked with some directories, also know as mounting file system.
- In unix Every think is a file or process. So device can also be represented with file located in /dev directory.

Directories in Root (/)
/bin: Essential Command binaries like cp, mv
/boot: contains files related to boot loader
/dev: Contains device files
/lib: Essential shared libraries and kernel modules
/media: mount point for removable media
/mnt: Mount point for mounting a file system temporarily
/opt: Add-on application software packages
/sbin: Essential system binaries
/srv Data for services provided by the system (usually found in Suse and Debian system)
/tmp: temporary files
/usr secondary hierarchy, most of the application programs are installed in /usr directories
/var: variable data.
/proc: virtual files system, which is used to store kernel parameter files temporarily

Accessing into Linux System
- Two type of logins:
  - Virtual Consoles (6 text base terminals available)
  - Graphical logins (1 GUI Display manager)
- Requires user name and password (root is a super user or administrator)
- Each user has a home directory
- Switching Terminal:
  - Press “Alt+F1 to F6” to access Text mode or virtual terminal in most Linux system.
  - Press “Ctrl+Alt+ F1 to F6” from GUI mode to access virtual terminal.
  - Press “Alt+F7” to access GUI, (in some Linux system like Fedora, “Alt+F1” will switch to GUI mode. Alternatively, starx command can be typed in console to access GUI screen or “init 5” can be executed in console.
- Switching between users
- A user can switch to another by typing ‘su – <username>’, where – option will reset the OS environment as per setting for switched user <username>. For example, “su – shiba” will switched to user name shiba. However, switching to root user don’t require to provide user’s name (i.e. “su -”).
Note: in Lab environment where students don’t have their own Linux system can access Linux Virtual Machine with SSH clients like Putty, Xshell and SecureShell etc. for following Lab exercises.
What is shell
- Shell is a interactive user interface between the user and the kernel to execute program or application in an OS. BASH is one of the most popular shell available in Linux/Unix system.
Starting with shell
- pwd: prints name of current working directory.

Using help
- man <command_name>: provides detail manual of particular command (e.g. #man ls)
- <command_name> –help : provides brief command options and parameters. (e.g. #ls –help). Most of the unix command also accesp -h option for help, but in some commands like in ls command. In some commands like ls and du, -h options is provided for human readable content display.
- Info <command_name>: it is an alternative help line for man and –help option.
- Documentation: most of the document available with application are stored in /usr/share/doc directory
Linux command and configurations based on RHCE certification:
Linux Note 1 Linux Note 2 Linux Note 3 Linux Note 4 Linux Note 5 Linux Note 6 Linux Note 7
References:
Source [1]: http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/c23.html
Source [2]: RH033 Red Hat Linux Essentials.