File System Hierarchy

File System Hierarchy#

Introduction#

The Linux file system has a hierarchical structure. Unlike Windows, which uses letters (C:, D:, etc.) to represent different drives, Linux uses a single directory / as the root of the entire file system. All files and directories are stored, logically, in the / directory.

Absolute and Relative Paths#

An absolute path is a path that starts from the root directory /. For example, /home/user1 is an absolute path. A relative path is a path that starts from the current directory. For example, home/user1 is path relative to the working directory.

Common Directories#

The File System Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix-like operating systems. The FHS is maintained by the Linux Foundation.

The following are some common directories in the Linux file system:

  • /home: This directory contains the home directories of all users. That includes your home directory.

  • /root: This is the home directory of the root user. It is only accessible by the superuser.

  • /bin: This directory contains essential system binaries. Common commands like ls, cp, and mv are stored here.

  • /sbin: This directory contains essential system binaries that are used by the superuser.

  • /usr: This directory contains user binaries, libraries, and documentation. This is not to be confused with the /home directory.

  • /etc: This directory contains system-wide configuration files.

  • /mnt: Mount point for mounting a filesystem temporarily.

Permissions#

Linux has a robust permission system that controls who can access files and directories.

When you list files with ls -l, you will see the details of files and directories. For example,

User@Machine:~$ ls -la
drwxrwxr-x  3 User staff 4096 Feb 16 22:04 .github

shows the info of the .github folder, which is owned by the user User and the group staff. 3 is the number of links to the directory. 4096 is the size of the directory itself in bytes.

drwxrwxr-x is the permission string:

  • The first character indicates the type of the file. d for directory, - for a regular file.

  • The next three characters are the owner’s permissions. The owner can read, write, and execute the file.

  • The next three characters are the group’s permissions. The group can read, write, and execute the file.

  • The last three characters are the other users’ permissions. They can read, and execute the file but cannot write.

The permission string is also represented in octal format with three in a group. rwxrwxr-x is 775 in octal.

Changing Permissions#

The chmod command is used to change the permissions (mode bits) of a file or directory. The format is chmod MODES FILES. For example,

User@Machine:~$ chmod 755 file.txt

removes the write permission for the group and others.

Permissions can be changed recursively with the -R flag. For example,

User@Machine:~$ chmod -R 755 folder

changes the permissions of the folder and all its contents.

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