How to create a filesystem on a Linux partition or logical volume

How to create a filesystem on a Linux partition or logical volume

Learn to create a filesystem and mount it persistently or non-persistently in your system.

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In computing, a filesystem controls how data is stored and retrieved and helps organize the files on the storage media. Without a filesystem, information in storage would be one large block of data, and you couldn't tell where one piece of information stopped and the next began. A filesystem helps manage all of this by providing names to files that store data and maintaining a table of files and directories—along with their start/end location, total size, etc.—on disks within the filesystem.

In Linux, when you create a hard disk partition or a logical volume, the next step is usually to create a filesystem by formatting the partition or logical volume. This how-to assumes you know how to create a partition or a logical volume, and you just want to format it to contain a filesystem and mount it.

Create a filesystem

Imagine you just added a new disk to your system and created a partition named /dev/sda1 on it.

  1. To verify that the Linux kernel can see the partition, you can cat out /proc/partitions like this:
    [root@localhost ~]# cat /proc/partitions
    major minor  #blocks  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
  1. Decide what kind of filesystem you want to create, such as ext4, XFS, or anything else. Here are a few options:
    [root@localhost ~]# mkfs.<tab><tab>
    mkfs.btrfs   mkfs.cramfs  mkfs.ext2     mkfs.ext3       mkfs.ext4       mkfs.minix   mkfs.xfs
  1. For the purposes of this exercise, choose ext4. (I like ext4 because it allows you to shrink the filesystem if you need to, a thing that isn't as straightforward with XFS.) Here's how it can be done (the output may differ based on device name/sizes):
    [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
  1. In the previous step, if you want to create a different kind of filesystem, use a different mkfs command variation.

Mount a filesystem

After you create your filesystem, you can mount it in your operating system.

  1. First, identify the UUID of your new filesystem. Issue the blkid command to list all known 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 ~]#
  1. 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 df -h command shows which filesystem is mounted on which mount point. Look for /dev/sd1. The mount command above used the device name /dev/sda1. Substitute it with the UUID identified in the blkid command. Also, note that a new directory was created to mount /dev/sda1 under /mnt.

  1. A problem with using the mount command directly on the command line (as in the previous step) is that the mount won't persist across reboots. To mount the filesystem persistently, 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
  1. After you edit /etc/fstab, you can umount /mnt/mount_point_for_dev_sda1 and run the command mount -a to mount everything listed in /etc/fstab. If everything went right, you can still list df -h and see your filesystem mounted:
    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
  1. You can also check whether the filesystem was 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 a filesystem and mount it persistently or non-persistently within your system. 

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About the author

Kedar Vijay Kulkarni - Kedar is a Software Quality Engineer at Red Hat working with CloudForms(upstream ManageIQ) project and primarily looking at deployment/management of our internal infrastructure. Interested in Jenkins Pipeline and Ansible for automating deployments. Also writing Shinken modules for Monitoring and Alerting. In his free time he likes to Travel, watch interesting videos, learn about new technologies.