Mounting and Unmounting Filesystems in Linux

In Linux, a filesystem isn’t part of the directory tree until it’s mounted. Mounting connects the filesystem (residing on an external disk, USB, or other storage device) to a directory so it can be accessed like any other folder. Unmounting disconnects it safely, ensuring all data is written and no processes are actively using it.

Many essential Linux filesystems are mounted automatically at boot and remain part of the tree during normal operation. These include the root /, /boot, /home, /var, and /usr. When you open / or browse /home, you’re already interacting with these mounted filesystems. Manual mounting is usually only needed for additional drives, removable media, or special-purpose filesystems.

Note: In our example, /dev/sdb1 is just a generic placeholder for a secondary device. It could be a USB drive, external HDD/SSD, or a second internal disk. The number (1) refers to the partition on that device.

The Linux kernel sees external devices like /dev/sdb1 as raw storage. You can’t browse /dev/sdb1 directly because it’s just a block device. Mounting maps that device to a directory, for example /mnt/usb, making its files accessible. Without mounting, the data exists but isn’t reachable in the filesystem hierarchy.

In the diagram below, the arrow shows the mounting process, linking it to a mount point in the filesystem tree. Once mounted, the device’s files appear under /mnt/mydisk and can be accessed like any other directory.

On most modern Linux desktops, USB drives and other removable devices are automatically mounted when you plug them in. The system chooses a mount point, usually under /media/username/ or /run/media/username/, and sets the permissions so you can access the files immediately.

Still, the manual mkdir + mount workflow is important to understand. You might need it when a device isn’t automatically recognized, when working on a headless system without a GUI, or when you want to mount a device at a custom location or with specific options like read-only (ro) or specifying a filesystem type. Understanding the manual process also helps you troubleshoot issues when automatic mounting fails.

Create a mount point (an empty directory):

sudo mkdir /mnt/mydisk

Mount the filesystem to that directory:

sudo mount /dev/sdb1 /mnt/mydisk

Now /mnt/mydisk contains the files from /dev/sdb1. You can now read, write, and modify them.

Unmounting safely -

Before removing a disk or shutting down certain filesystems, you must unmount:

sudo umount /mnt/mydisk

Unmounting ensures all cached writes are flushed to disk. If a filesystem is in use (a terminal inside it, an open file, a running program), unmounting will fail. The lsof or fuser commands help identify what’s keeping it busy.

Mounting is the bridge between a raw storage device and the Linux filesystem tree. Unmounting closes that bridge safely. Most of the time, important filesystems are mounted automatically, but knowing how to mount and unmount manually gives you control over additional drives, removable media, and troubleshooting.

Linux Learning Series - Ben Santora - January 2026