Filesystem Hierarchy

In this article, we explore the Linux filesystem hierarchy, detailing the structure and purpose of various directories. Dave explains the layout while Bob listens attentively.

Key Directories and Their Purposes

• /home
This directory holds the home directories for all users except the root user. The root user’s home directory is located at /root.

• /opt
Third-party programs are typically installed here. For example, if you are deploying the web application for Project Mercury, /opt is the ideal installation location.

• /mnt and /tmp
When setting up Bob’s laptop, Dave recommends installing security-mandated software. The software packages are stored in a repository on the company's network share. Dave mounts this repository temporarily at /mnt using the mount command, then copies the necessary packages to /tmp.

After the installation, Dave unmounts the network share from /mnt and deletes the temporary files in /tmp.

• /media
Bob notices that when he plugs in a USB drive, Linux automatically mounts it under /media (unlike Windows, which might assign it a drive letter like G:). This directory is reserved for all external media.

• /dev
The /dev directory contains special block and character device files. These files represent hardware devices such as external hard disks, mice, keyboards, and more.

• /bin and /etc
Dave explains that essential programs and binaries (like cp, mv, mkdir, and date) reside in /bin. Meanwhile, /etc is crucial because it stores the majority of Linux configuration files.

• /lib and /lib64
These directories store shared libraries required by programs during runtime.

• /usr
Modern Linux systems use /usr to store userland applications and their data. Historically, user home directories were located here. This directory contains software such as the Thunderbird mail client, Mozilla Firefox, and the vi editor.

• /var
When system or application issues arise, logs and cached data stored in /var can provide essential troubleshooting insights.

Inspecting Mounted Filesystems

To view details about each mounted filesystem, Dave demonstrates the df command. The following example shows the command output:

[~]$ df -hP
Filesystem      Size  Used Avail Use% Mounted on
udev            3.8G     0  3.8G   0% /dev
tmpfs           783M  1.6M  781M   1% /run
/dev/sda3       43G   36G  7.3G  84% /
tmpfs           3.9G  128K  3.9G   1% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
/dev/sda5       20G    1G   19G   5% /home
/dev/sda4       10G    5G    5G  50% /var
/dev/sdb1       5G     1G    4G  20% /media/usb

In this output, Bob observes that his USB drive is mounted under /media and is referenced by the device path /dev/sdb1.

Before moving on, let's put these concepts into practice and solidify your understanding of the Linux filesystem hierarchy.