Linode Manager always says Disk is full

The storage breakdown in the Linode Manager is not actually referring to how full your disk is, but rather how much of your plan's total storage allotment is currently allocated to disks. In most cases, you will have a swap disk and your main disk, which together take up 100% of your plan's storage allocation. If you were to upgrade your plan or resize your disk to a smaller size, then that number would change. You could then allocate that space to another disk, or in the case of a plan upgrade, you could make your existing disk larger.

As we are primarily an infrastructure provider, we do not have the ability to see into your Linode's internals, and so we cannot tell how full a particular disk is from our end. The df command is the correct way to view your disk's usage, and the -h, or --human-readable flag will ensure that the output is easy to read:

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            463M     0  463M   0% /dev
tmpfs            99M  8.3M   91M   9% /run
/dev/sda         25G  4.3G   19G  19% /
tmpfs           493M     0  493M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           493M     0  493M   0% /sys/fs/cgroup
tmpfs            99M     0   99M   0% /run/user/5005