We cannot yet mount or interact with the partitions we have created. This is because we have not added a filesystem to each partition.
> A filesytem is a form of [database](/Databases/Basic_database_concepts.md); it supplies the structure to transform a simple block device into the sophisticated hierarchy of files and subdirectories that users can understand.
Linux recognises many types of filesystems. The native Linux filesystem is the **ext4** (Fourth Extended Filesystem). Another common filesystem is **FAT** (File Allocation Table). Instances of this include _MSDOS_,_EXFAT_,_FAT-32_. They originate from Microsoft systems
## Creating a filesystem
Remember we have two partitions on our external drive: `sda1` and `sda2`. We are going to use the `mkfs` utility to create an EXT4 system on both.
```bash
mkfs -t ext4 /dev/sda1
mkfs -t ext4 /dev/sda2
```
## Mounting a filesystem
We can now mount our filesystems. Whem we mount, we must specify the following criteria with the request:
* The name of the device we want to mount.
* This will be the name or the partition. However the names (`sda` etc) assigned by the OS can change. In these cases and with GPT-based partitions you can use the UUID.
* To see a list of devices and the corresponding filesystems and UUIDs on your system, you can use the **`blkid`** ('block id') program.
* This is the place within the existing filesystem where you want to mount the partition.
* When you mount to a directory, this directory _becomes_ the disk you have mounted, you will not see it as a subdirectory within the the mount point, you will just see the contents of the disk itself
```bash
mkdir mountpoint
mount -t ext4 /dev/sda1 /mnt
touch test.txt
```
Our `sda1` partition is now mounted at `mountpoint`. We can go ahead and create files. If we now look within the graphical file manager when we click on the `sda1` volume, we will see the new file we have created in `mountpoint`.
