Directory Structure

what is ~ directory in linux and how is it different than root directory / ? In Linux, the tilde (~) character is a shorthand or alias for the current user's home directory. It provides a quick way to refer to the home directory of the user who is currently logged in. Here's a bit more detail:

The ~ Directory

• Usage: When you type ~ in the shell, it is automatically expanded by the shell to the path of the home directory of the user who is currently logged in. For example, if you are logged in as a user named "john", typing cd ~ or just cd will take you to /home/john.

• Context-Sensitive: If used in conjunction with another user's name, such as ~username, it expands to that user's home directory. For instance, ~john would expand to /home/john.

Differences Between ~ and / (Root Directory)

• Meaning and Use:

  • The ~ symbol specifically refers to user home directories, making it a user-centric pointer within the filesystem.

  • The / symbol represents the root directory of the entire filesystem hierarchy. It is the very top level of the filesystem and contains all other files and directories in the system.

• Purpose:

  • The ~ directory is used primarily for storing a user's personal files, configurations, and directories in a segregated manner. Each user has their own ~ directory, isolated from other users (except for those with administrative privileges).

  • The root directory / is used to structure the entire system's filesystem, holding system and application files necessary for the operation of the entire system. It includes directories such as /bin, /etc, /dev, /usr, and more, which are crucial for system operations and shared among all users.

• Permissions:

  • Access to ~ (i.e., a user’s home directory like /home/john) is generally restricted to the user itself and the system administrator. This helps in maintaining privacy and security for user-specific data.

  • Access to / and many of its subdirectories needs to be more controlled as they contain system-wide configurations and executable binaries. Some subdirectories under / are writable only by the root user (superuser), ensuring system integrity and security.

In summary, ~ is personalized and specific to each user, referring to their home directory, whereas / is universal to the Linux system, referring to the top-level directory under which the entire filesystem is organized.

Certainly! The directory structure of a Linux system is hierarchical and follows a specific standard known as the Filesystem Hierarchy Standard (FHS). This standard defines the main directories and their contents in Linux operating systems. Here’s an overview of the key directories and their functions:

1. / (Root)

• Description: The root directory is the top level of the file system hierarchy. Every other directory and file on the system is under the root directory, although they may be on different physical or virtual devices.

2. /bin

• Description: Contains essential binary executables (programs) that are needed in single-user mode and for performing basic system tasks.

• Examples: bash, ls, cat, etc.

3. /sbin

• Description: Like /bin, but contains binaries essential for booting, restoring, recovering, and/or repairing the system in addition to those required for system administration.

• Examples: init, ip, fsck, etc.

4. /boot

• Description: Holds files used in booting the operating system, including the Linux kernel itself, and usually the initial RAM disk (initrd or initramfs), which contains tools and scripts needed to boot the system.

• Examples: vmlinuz (Linux kernel), grub (GRUB boot loader).

5. /dev

• Description: Contains device files which represent and provide access to hardware devices (like hard drives, sound devices, etc.) and some software devices.

• Examples: /dev/sda (first SATA drive), /dev/null, /dev/tty (terminal devices), etc.

6. /etc

• Description: Contains configuration files required by all programs. This directory only contains static configuration files, which do not change without administrator intervention.

• Examples: /etc/passwd (user account info), /etc/fstab (disk mount points), /etc/network/interfaces, etc.

7. /home

• Description: Contains the personal directories of all users who have accounts on the system, except for the root user.

• Examples: /home/username

8. /lib, /lib64

• Description: Contains essential shared libraries and kernel modules needed to boot the system and run the commands in the root filesystem.

• Examples: Libraries like libc.so.6, kernel modules like *.ko.

9. /media

• Description: Mount point for removable media such as USB drives, CD-ROMs, etc.

• Examples: /media/cdrom, /media/usb

10. /mnt

• Description: Temporarily mounted filesystems. Often used as a temporary mount point for mounting a file system as needed.

• Examples: /mnt/cdrom, /mnt/backup

11. /opt

• Description: Optional application software packages. Often where third-party software gets installed.

• Examples: /opt/chrome, /opt/vmware

12. /proc

• Description: A virtual filesystem provided by the kernel that contains runtime system information (e.g., system memory, devices mounted, hardware configuration, etc.).

• Examples: /proc/cpuinfo, /proc/meminfo

13. /root

• Description: The home directory of the root user (superuser). Separate from /home for security and because it is not on a network file system.

• Examples: /root/.bashrc

14. /run

• Description: A temporary filesystem that stores transient state files since the last boot. It's used to keep runtime data for processes started since the last boot.

• Examples: /run/udev or /run/sshd.pid

15. /srv

• Description: Contains data which is served by the system.

• Examples: /srv/http, /srv/ftp

16. /tmp

• Description: Temporary files (often not preserved between system reboots).

• Examples: Various temporary files used by applications.

17. /usr

• Description: Secondary hierarchy for user data; contains the majority of (multi-)user utilities and applications.

• Subdirectories:

  • /usr/bin: Non-essential command binaries (not needed in single user mode).

  • /usr/sbin: Non-essential system binaries, like various daemons for network services.

  • /usr/lib, /usr/lib64: Libraries for /usr/bin and /usr/sbin.

  • /usr/local: Tertiary hierarchy for local data; specific to this host. Typically has further subdirectories, such as bin, sbin, lib, share.

18. /var

• Description: Variable files—files whose content is expected to continually change during normal operation of the system—such as logs, spool files, and temporary e-mail files.

• Examples: /var/log, /var/spool/mail, /var/tmp

This structure helps with system organization, security, and compatibility. Different sections of the filesystem are mounted with different settings to secure the system and separate out user data, system data, transient data, and static data.