How to create a file system in a Linux partition or logical volume

Preface

Learn to create a file system on your system and mount it either persistently or non-persistently.

In computing, a file system controls how data is stored and retrieved and helps organize files on storage media. Without a file system, information would be stored as one large block of data, and you would have no way of knowing where one piece of information ended and the next began. The file system helps manage all of this information by providing names for the files that store data and maintaining a table of files and directories on disk in the file system along with their start and end locations, total size, and so on.

In Linux, after you create a hard disk partition or logical volume, the next step is usually to create a file system by formatting the partition or logical volume. This how-to assumes that you already know how to create a partition or logical volume, and that you want to format it to include a file system and mount it.

Creating a file system

Suppose you added a new hard disk to your system and created a partition on it called /dev/sda1.

1. To verify that the Linux kernel has discovered the partition, you can cat the contents of /proc/partitions, like this:

[root@localhost ~]# cat /proc/partitions
major minor #block name

 253 0 10485760 vda
 253 1 8192000 vda1
 11 0 1048575 sr0
 11 1 374 sr1
 8 0 10485760 sda
 8 1 10484736 sda1
 252 0 3145728 dm-0
 252 1 2097152 dm-1
 252 2 1048576 dm-2
 8 16 1048576 sdb

2. Decide what kind of file system you want to create, such as ext4, XFS, or something else. Here are some options:

[root@localhost ~]# mkfs.<tab><tab>
mkfs.btrfs mkfs.cramfs mkfs.ext2 mkfs.ext3 mkfs.ext4 mkfs.minix mkfs.xfs

3. For the purpose of this exercise, choose ext4. (I like ext4 because it allows you to compress the filesystem if you need it, which is not easy with XFS.) Here's how to do it (the output may vary depending on the device name or size):

[root@localhost ~]# mkfs.ext4 /dev/sda1
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=8191 blocks
194688 inodes, 778241 blocks
38912 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=799014912
24 block groups
32768 blocks per group, 32768 fragments per group
8112 inodes per group
Superblock backups stored on blocks:
  32768, 98304, 163840, 229376, 294912

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

4. In the previous step, if you want to create a different file system, use a different variant of the mkfs command.

Mounting the file system

Once you have created the file system, you can mount it in your operating system.

1. First, identify the UUID code of the new file system. Use the blkid command to list all recognized block storage devices and look for sda1 in the output:

[root@localhost ~]# blkid
/dev/vda1: UUID="716e713d-4e91-4186-81fd-c6cfa1b0974d" TYPE="xfs"
/dev/sr1: UUID="2019-03-08-16-17-02-00" LABEL="config-2" TYPE="iso9660"
/dev/sda1: UUID="wow9N8-dX2d-ETN4-zK09-Gr1k-qCVF-eCerbF" TYPE="LVM2_member"
/dev/mapper/test-test1: PTTYPE="dos"
/dev/sda1: UUID="ac96b366-0cdd-4e4c-9493-bb93531be644" TYPE="ext4"
[root@localhost ~]#

2. Run the following command to mount the /dev/sd1 device:

[root@localhost ~]# mkdir /mnt/mount_point_for_dev_sda1
[root@localhost ~]# ls /mnt/
mount_point_for_dev_sda1
[root@localhost ~]# mount -t ext4 /dev/sda1 /mnt/mount_point_for_dev_sda1/
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 7.9G 920M 7.0G 12% /
devtmpfs 443M 0 443M 0% /dev
tmpfs 463M 0 463M 0% /dev/shm
tmpfs 463M 30M 434M 7% /run
tmpfs 463M 0 463M 0% /sys/fs/cgroup
tmpfs 93M 0 93M 0% /run/user/0
/dev/sda1 2.9G 9.0M 2.7G 1% /mnt/mount_point_for_dev_sda1
[root@localhost ~]#

The command df -h shows the mount point where each file system is mounted. Find /dev/sd1. The device name used in the mount command above is /dev/sda1. Replace it with the UUID code in the blkid command. Note that a newly created directory under /mnt is mounted as /dev/sda1.

3. Using the mount command directly from the command line (just like in the previous step) will result in the mount not persisting after the device is rebooted. To mount the file system permanently, edit the /etc/fstab file to include your mount information:

UUID=ac96b366-0cdd-4e4c-9493-bb93531be644 /mnt/mount_point_for_dev_sda1/ ext4 defaults 0 0

4. After editing the /etc/fstab file, you can umount /mnt/mount_point_for_fev_sda1 and run the mount -a command to mount all the device files listed in the /etc/fstab file. If all goes well, you can use df -h to list and view your mounted filesystems:

root@localhost ~]# umount /mnt/mount_point_for_dev_sda1/
[root@localhost ~]# mount -a
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 7.9G 920M 7.0G 12% /
devtmpfs 443M 0 443M 0% /dev
tmpfs 463M 0 463M 0% /dev/shm
tmpfs 463M 30M 434M 7% /run
tmpfs 463M 0 463M 0% /sys/fs/cgroup
tmpfs 93M 0 93M 0% /run/user/0
/dev/sda1 2.9G 9.0M 2.7G 1% /mnt/mount_point_for_dev_sda1

5. You can also check whether the file system is mounted:

[root@localhost ~]# mount | grep ^/dev/sd
/dev/sda1 on /mnt/mount_point_for_dev_sda1 type ext4 (rw,relatime,seclabel,stripe=8191,data=ordered)

Now you know how to create file systems and mount them on your system either permanently or temporarily.

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