Linux Root File System

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Linux offers two types of file systems for use. One is called ext2 (i.e. the Extended-2 File System) the other is called the ext3 File System. The organization of directories in the file system is hierarchical. / (the root directory) is the upper most directory in this structure.

Any storage device, to which data is read or written must be included in the file system and has to be mounted into a directory. Removable media devices like CDROM, Tape, floppy drives and so on, have to be mounted into file system only after the media is inserted into the relevant drive.

Non-removable media devices like HDD are normally auto mounted at boot-time (as described in /etc/fstab file).

The following are the directories that are created by default, once Linux is installed.

/bin:	This directory holds binary executable files & common Linux user commands.
/dev:	This holds device definitions & contains files representing access points to devices on your system. Users normally access these devices directly through the device files.
/home:	This is the working directory of ordinary users. Contains directories assigned to each user with login account.
/root:	This is the working directory of super user i.e., home directory of super user.
/var:	This holds variable information. Like login messages, mail messages, booting messages etc.
/boot:	This directory holds bootable files.
/etc:	This directory contains administrative configuration commands & files. In order to obtain the services like samba, apache etc. we require some configuration files all of which will be under this directory.
/lib:	This holds library files. These files hold inbuilt device drivers for all your hardware devices.
/mnt:	This directory provides a location for mounting devices, such as remote file systems & removable devices (cdrom, floppy etc).
/proc:	This directory provides an interface between kernel data structure & your system.
/sbin:	This holds binary executable files & this files are accessible by only super user or root user. This directory also contains administrative commands.
/usr:	This directory contains user documentation, games, graphical files (X11),& variety of other user & administrative commands & files.
/lost+found:	All files lost during an abnormal shutdown (like a power failure) or system crash are saved under this directory.
/opt:	This is purely optional directory wherein new packages could be installedas otherwise it is empty.
/tmp:	This is temporary directory wherein certain files get written into during installation of packages (Installation log).

Important properties of files and directories

Files or directories can have names that are up to 255 characters in length. Meta characters such as *,?,&,$,# and so on cannot be used in file and directory names .

In Linux the concept of file name extensions simply does not exist. The characters after aperiod (.) in a file name is only used for the purpose of characterizing (simply adding to the meaning of a file name nothing more) the file type (like . conf).

The period . is also part of the file name. There can be several periods in a file name. If a file or a directory name starts with a period . it becomes a hidden file or directory.

Every file / directory has a total of 9 permission levels - read, write, execute, with respect to its user (owner), group and others who can access the file or directory.

Every file / directory has two ownerships, user-ownership and group-ownership.

A normal user has permission to read/write in their home directory, read permission in the entire directory structure except the home directories of other users, including root and proc directory.

The root user has permission to read / write anywhere in the file system except write permission in proc directory .