How to format disks and partitions in Linux

Formatting disks and partitions in Linux prepares storage for reliable data use, removes obsolete filesystem structures, and aligns space usage with new workloads. Correct formatting is especially important when reusing drives from other systems or converting removable media for use with Linux tools. Choosing an appropriate filesystem also affects performance, maximum file sizes, and compatibility with other operating systems.

Under Linux, the family of mkfs utilities creates filesystems on block devices such as /dev/sda2 or /dev/sdb1. Each filesystem type has a dedicated helper, for example mkfs.ext4 for ext4, mkfs.btrfs for Btrfs, or mkfs.vfat for FAT32 and exFAT. The selected helper writes superblocks, allocation tables, journals, and other on-disk structures that define how files and directories are stored.

Formatting always overwrites an existing filesystem and destroys the data stored on it. Confirming the correct device name before running any mkfs command avoids damaging the system disk or other important volumes. Unmounting the target partition and ensuring that no services depend on it reduces the risk of corruption and guarantees a clean filesystem layout.

1. Open a terminal with sudo privileges.
2. List available disks and partitions and note device names and sizes.

   $ lsblk
   NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
   loop0    7:0    0   512M  0 loop /mnt/bench
   loop1    7:1    0   300M  0 loop /mnt/format-prep
   nbd0    43:0    0     0B  0 disk 
   nbd1    43:32   0     0B  0 disk 
   nbd2    43:64   0     0B  0 disk 
   nbd3    43:96   0     0B  0 disk 
   nbd4    43:128  0     0B  0 disk 
   nbd5    43:160  0     0B  0 disk 
   nbd6    43:192  0     0B  0 disk 
   nbd7    43:224  0     0B  0 disk 
   vda    254:0    0   1.8T  0 disk 
   `-vda1 254:1    0   1.8T  0 part /etc/hosts
                                    /etc/hostname
                                    /etc/resolv.conf
   vdb    254:16   0 606.5M  1 disk 
   nbd8    43:256  0     0B  0 disk 
   nbd9    43:288  0     0B  0 disk 
   nbd10   43:320  0     0B  0 disk 
   nbd11   43:352  0     0B  0 disk 
   nbd12   43:384  0     0B  0 disk 
   nbd13   43:416  0     0B  0 disk 
   nbd14   43:448  0     0B  0 disk 
   nbd15   43:480  0     0B  0 disk 

   The NAME column maps to device paths such as /dev/loop1, while SIZE and MOUNTPOINTS help identify the intended disk.

3. Confirm the exact device intended for formatting using size and mountpoint information.

   $ df -h /root
   Filesystem      Size  Used Avail Use% Mounted on
   overlay         1.8T   17G  1.7T   1% /

   Formatting the wrong device such as /dev/vda instead of a loop device permanently destroys the existing filesystem and its data.

4. Unmount the target partition if a mountpoint is listed in lsblk or df output.

   $ sudo umount /dev/loop1

   No output from umount indicates the partition is now detached.

5. Verify that the target partition is no longer mounted.

   $ lsblk /dev/loop1
   NAME  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
   loop1   7:1    0  300M  0 loop 

6. List available filesystem-specific mkfs helpers on the system.

   $ ls /sbin/mkfs.*
   /sbin/mkfs.bfs
   /sbin/mkfs.cramfs
   /sbin/mkfs.ext2
   /sbin/mkfs.ext3
   /sbin/mkfs.ext4
   /sbin/mkfs.minix

   Typing mkfs. and pressing <TAB> twice in many shells shows the same helpers via completion.

7. Format the target partition with the desired filesystem type and optional label.

   $ sudo mkfs.ext4 -F -L data /dev/loop1
   mke2fs 1.47.0 (5-Feb-2023)
   Discarding device blocks:     0/76800           done                            
   Creating filesystem with 76800 4k blocks and 76800 inodes
   Filesystem UUID: 71cbb0a9-ef27-4ce6-98e9-1f67d2fea5cf
   Superblock backups stored on blocks: 
   	32768
   
   Allocating group tables: 0/3   done                            
   Writing inode tables: 0/3   done                            
   Creating journal (4096 blocks): done
   Writing superblocks and filesystem accounting information: 0/3   done

   Running mkfs.ext4 on an existing partition erases all contained files and directories and cannot be undone.

8. Check the new filesystem type and UUID for the formatted partition.

   $ sudo blkid /dev/loop1
   /dev/loop1: LABEL="data" UUID="71cbb0a9-ef27-4ce6-98e9-1f67d2fea5cf" BLOCK_SIZE="4096" TYPE="ext4"

   The UUID value is suitable for use in /etc/fstab to configure persistent mounts.

9. Create a temporary mountpoint directory for the new filesystem.

   $ sudo mkdir -p /mnt/format-demo

10. Mount the new filesystem on the temporary mountpoint.

    $ sudo mount /dev/loop1 /mnt/format-demo

    For permanent configuration, define a dedicated mountpoint and a corresponding entry in /etc/fstab as described in How to mount disks and partitions in Linux.

11. Verify that the mounted filesystem is accessible and initially empty.

    $ ls -A /mnt/format-demo
    lost+found
    $ df -h /mnt/format-demo
    Filesystem      Size  Used Avail Use% Mounted on
    /dev/loop1      265M   24K  244M   1% /mnt/format-demo

12. Unmount the filesystem again if the temporary mount is no longer required.

    $ sudo umount /mnt/format-demo