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What is Ext4 file system?

The ext4 or fourth extended filesystem is a widely-used journaling file system for Linux. The ext4 file system is a scalable extension of the ext3 file system. It was designed as a progressive revision of the ext3 file system and overcomes a number of limitations in ext3.

After installation, it is sometimes necessary to create a new file system. For example, if you add a new disk drive to the system, you may want to partition the drive, and use the ext4 file system.

Some prerequisites for this blog are:

1. I assumed that you have added a new hard drive or pen drive to your Linux machine, in which you will create the new ext4 partition, and
2. Run all the command as a root user.

Creating an Ext4 file system

1. First list the partition by using fdisk -l or parted -l commands to identify the hard drive you want to partition.
   I am using my 16GB pen-drive and I will make it as a drive in my system.

$ parted -l

Output for the above command is:

 Model: ATA WDC WD5000LPCX-6 (scsi)
 Disk /dev/sda: 500GB
 Sector size (logical/physical): 512B/4096
 Partition Table: gpt
 Disk Flags: 

 Number  Start   End    Size   File system  Name                  Flags
 1      1049kB  538MB  537MB  fat32        EFI System Partition  boot, esp
 2      538MB   500GB  500GB  ext4


 Model: SanDisk Cruzer Blade (scsi)
 Disk /dev/sdb: 15.6GB
 Sector size (logical/physical): 512B/512B
 Partition Table: loop
 Disk Flags: 

 Number  Start  End     Size    File system  Flags
 1      0.00B  15.6GB  15.6GB  fat32

Looking at the output in the above output, we have one hard disk added to the system and we will have partition disk /dev/sdb with the name SanDisk Cruzer Blade (scsi) and its file system is fat-32.

Now we use parted command to start creating the partition on the selected storage device.

$ parted /dev/sdb

Output for the above command is:

GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.

Give the new disk a label using the mklabel command.

$ (parted) mklabel msdos

Output for the above command is:

Warning: Partition(s) on /dev/sdb are being used.
                                                                                                                                                                       Ignore/Cancel? Ignore   
 Warning: The existing disk label on /dev/sdb will be destroyed and all
data on this disk will be lost. Do you want to continue?
                                                                                                                                           
Yes/No? yes

Now create a partition using the mkpart command, give it additional parameters like “primary” or “logical” depending on the partition type that you wish to create. Now select ext4 as the file system type. Set the start and end to establish the size of the partition.

$ (parted) mkpart

Output for the above command is:

Partition type?  primary/extended? primary
File system type?  [ext2]? ext4
Start? 1
End? 14500
(parted) 

If you see we start the space from 1 and ended at 14500 because we need to leave some space for the “pre-allocating” the overhead. ext4 creates a lot of overhead before any files are created and it requires space to store that data.

To print the partition table on the device /dev/sdb or detailed information about the new partition, run the print command.

$ (parted) print

Output for the above command is:

Model: SanDisk Cruzer Blade (scsi)
Disk /dev/sdb: 15.6GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

 Number  Start   End     Size    Type     File system  Flags
    1      1049kB  14.5GB  14.5GB  primary  ext4         lba

Now exit the program using the quit command.

Formatting New Ext4 Partition

Next, you need to properly format the new partition with the ext4 file system type using the mkfs or mke4fs command as follows.

$ mkfs.ext4 /dev/sdb1

Output for the above command is:

mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 3539712 4k blocks and 885952 inodes
Filesystem UUID: 99ba66f4-e976-492a-9d77-1b5bc6640400
Superblock backups stored on blocks: 
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done   

We can label the partition using the e4label and e2label commands as follows.

$ e2label /dev/sdb1 disk2-part1

Mounting New Ext4 Parition in File System

Next, create a mount point and mount the newly created partition file system.

 $ mkdir /mnt/disk2-part1
 $ mount /dev/sdb1 /mnt/disk2-part1

Now we are using df command to list all file systems on our system together with their sizes in a human-readable format (-h), and their mount points and file system types (-T):

$ df -hT

Filesystem     Type      Size  Used Avail Use% Mounted on
udev           devtmpfs  1.7G     0  1.7G   0% /dev
tmpfs          tmpfs     340M  3.5M  336M   2% /run
/dev/sda2      ext4      457G   40G  394G  10% /
tmpfs          tmpfs     1.7G  392M  1.3G  24% /dev/shm 
tmpfs          tmpfs     5.0M  4.0K  5.0M   1% /run/lock
tmpfs          tmpfs     1.7G     0  1.7G   0% /sys/fs/cgroup
/dev/loop0     squashfs  2.3M  2.3M     0 100% /snap/gnome-system-monitor/145
/dev/loop8     squashfs   56M   56M     0 100% /snap/core18/1885
/dev/loop3     squashfs   83M   83M     0 100% /snap/scrcpy/238
/dev/loop7     squashfs  2.5M  2.5M     0 100% /snap/gnome-calculator/748
/dev/loop2     squashfs  162M  162M     0 100% /snap/gnome-3-28-1804/128
/dev/loop6     squashfs   97M   97M     0 100% /snap/core/9665
/dev/loop5     squashfs   83M   83M     0 100% /snap/scrcpy/243
/dev/loop9     squashfs   55M   55M     0 100% /snap/core18/1880
/dev/loop13    squashfs  291M  291M     0 100% /snap/vlc/1700
/dev/loop4     squashfs   55M   55M     0 100% /snap/gtk-common-themes/1502
/dev/loop10    squashfs   97M   97M     0 100% /snap/core/9804
/dev/loop11    squashfs  1.0M  1.0M     0 100% /snap/gnome-logs/93
/dev/loop14    squashfs  2.3M  2.3M     0 100% /snap/gnome-system-monitor/148
/dev/loop12    squashfs   63M   63M     0 100% /snap/gtk-common-themes/1506
/dev/loop1     squashfs  161M  161M     0 100% /snap/gnome-3-28-1804/116
/dev/loop15    squashfs  1.0M  1.0M     0 100% /snap/gnome-logs/100
/dev/loop17    squashfs  164M  164M     0 100% /snap/spotify/41
/dev/loop16    squashfs  384K  384K     0 100% /snap/gnome-characters/550
/dev/loop18    squashfs  4.4M  4.4M     0 100% /snap/gnome-calculator/704
/dev/loop19    squashfs  291M  291M     0 100% /snap/vlc/1620
/dev/loop20    squashfs  384K  384K     0 100% /snap/gnome-characters/539
/dev/sda1      vfat      511M  6.1M  505M   2% /boot/efi
    tmpfs          tmpfs     340M   20K  340M   1% /run/user/121
tmpfs          tmpfs     340M   72K  340M   1% /run/user/1000
tmpfs          tmpfs     340M     0  340M   0% /run/user/0
 /dev/sdb1      ext4       14G   41M   13G   1% /mnt/disk2-part1
    

The last entry is for our newly created ext4 filesystem and you can now use it to store your data.

=>/dev/sdb1      ext4       14G   41M   13G   1% /mnt/disk2-part1

Lastly, add the following entry in your /etc/fstab to enable persistent mounting of the file system, even after a reboot.

$ sudo vim /etc/fstab

    /dev/sdb1   /mnt/disk2-part1  ext4   defaults    0   0

Conclusion

In this blog, we show how to create a new ext4 file system (partition) and how to mount it. I hope this blog helps you with the creation and mounting of the ext4 file system even you can try by yourself to create an ext3 file system.