In this guide, we demonstrate how to shrink an LVM volume or partition in Linux by resizing the file system followed by resizing the logical volume.

Note: This example is based on CentOS 8. Commands may vary in different Linux distributions. As of CentOS 8, the default file system is XFS, which cannot be shrunk. This guide focuses on the ext4 file system.

Overview of Logical Volume Manager (LVM):

Before diving into the resizing process, it’s crucial to understand some basic concepts:

• Physical Volume (PV): Created on a physical disk or Linux partition.
• Volume Group (VG): Consists of one or more physical volumes.
• Logical Volume (LV): Also known as the partition, resides within a volume group and hosts a file system.
• File System: e.g., ext4, exists on the logical volume.

How to Decrease or Shrink the Logical Volume:

To reduce the size of an LVM partition, you must initially decrease the file system within to prevent potential data corruption. Due to the risk involved in mistyping commands, it’s highly advised to create a full backup of your data beforehand. Shrinking a logical volume creates additional space in the volume group, allowing you to potentially extend another logical volume using this newfound space.

The initial step varies based on whether you intend to shrink an LVM root volume or a non-root volume.

vgchange -a y

umount /dev/centos/var

e2fsck -fy /dev/centos/var

Subsequently, you’ll need to reduce the size of the file system. For safety, we’ll shrink the file system to a size lower than what the logical volume will shrink to. This precaution prevents accidental shrinking of the logical volume to a size smaller than the file system, which could lead to corruption and data loss. Rest assured, we’ll reclaim the space later in the process.

The following command will shrink the file system to a total size of 4G. It’s important to note that the specified size for shrinking must have available free space within the file system. If there isn’t enough free space, data deletion may be necessary before proceeding.

resize2fs /dev/centos/var 4G

After reducing the file system, proceed to shrink the size of the logical volume using the lvreduce command. Adjust it to the desired volume size by specifying the -L flag. Alternatively, if you prefer reducing it by a specific size, prepend a ‘-‘ before the size. Both options are provided below for clarity, though you only need to execute one.

lvreduce -L 5G /dev/vg/disk-name

lvreduce -L -5G /dev/vg/disk-name

After executing the lvreduce command, you’ll receive a warning indicating the chosen size for reduction. Take this opportunity to ensure that you’re shrinking the logical volume to a size that is not smaller than the size you previously reduced the file system to. Once you’ve confirmed, proceed by entering ‘y’ and pressing enter.

Once the logical volume has been decreased to the desired size, execute resize2fs on the volume. This action extends the file system to utilize all available space within the logical volume, ensuring that none of the previously shrunk file system’s free space is wasted.

resize2fs /dev/centos/var

Now, the final step is to mount the volume. If it’s a root volume and you’re operating within a Live CD environment, just reboot into your primary Linux operating system.

For a non-root volume that was unmounted during the reduction process, simply remount it. You can accomplish this by using the command ‘mount -a’, assuming the configuration is already set in /etc/fstab. Alternatively, specify the logical volume and its mount point. In this example, we’re manually mounting it to /mnt for testing purposes.

mount /dev/centos/var /mnt

Once you’ve either rebooted into the primary operating system or completed the mount, verify the decreased space by using the ‘df’ command. This ensures that the reduction has been successfully applied as anticipated.

[root@hostname /]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root  9.8G  1.4G  8.5G  14% /
devtmpfs                 908M     0  908M   0% /dev
tmpfs                    914M     0  914M   0% /dev/shm
tmpfs                    914M  8.6M  905M   1% /run
tmpfs                    914M     0  914M   0% /sys/fs/cgroup
/dev/sda1                497M   96M  402M  20% /boot
/dev/mapper/centos-var  4.8G   20M  4.6G   1% /mnt

*In this instance, /dev/centos/var accurately reflects the reduction from the initial 10G size.

By following these simple steps you can shrink your LVM volume.