resize2fs is the tool that lets an ext4 filesystem use the extra space you’ve added to a partition. Without it, the partition may be larger, but the filesystem still sees the old size, so your available disk space won’t increase.
A common situation is extending a partition with fdisk or parted, then running df -h and noticing that the size hasn’t changed. That’s because only the partition was expanded, but the filesystem itself still needs to be resized. resize2fs takes care of that by expanding the ext4 filesystem to fill the newly available space.
In this guide, we’ll explain what resize2fs does, how to expand an ext4 filesystem after resizing a partition, and how to verify the change in Linux.