"No more space left on device" error

I would first check to see how much space your disks are actually using with the df command and -h flag to print sizes in human readable format:
df -h

If you are still out of space you can resize your disks to allocate more of your plans total disk space from the Linode Manager. If you've already allocated all of your plans disk space, you may want to cosinder utilizing our Block Storage to add more disk space to your Linode.

If lack of space turns out to not be the culprit, you may want to utilize the du command and specify the starting from the root directory /. This also assumes your are running as root.
du -h /

This will calculate how much total space your files are using. A large discrepancy in space used between the output of df and du could mean that some large file has been deleted, but is still opened by some process. If you take a look at the example from my Linode below you'll see the discrepancy is relatively small at 3.0GB and 3.7GB respectively.

root@localhost:~$ du -h /
....
15M    /bin
4.0K    /mnt
3.0G    /

root@localhost:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G     0  3.9G   0% /dev
tmpfs           798M  6.9M  791M   1% /run
/dev/sda         49G  3.0G   44G   7% /
tmpfs           3.9G     0  3.9G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
tmpfs           798M     0  798M   0% /run/user/1000

I came across this pretty good maketecheasier guide that goes over this issue in a little more detail, and you may find useful.

And your "limited user" (what is this exactly? in what ways is it limited? how?) is writing to same exact directory / volume as root user?

Maybe your non-root user has a disk quota (limit) set up - and which hasn't been increased?

A limited user is any user that is not root. Please note, limited users can still have super user permissions and may be able to perform any actions your root user can by adding the prefix sudo to any command.

Also you can limit a users use of disk space with quotas, however this has to be implemented, and you would probably know if you implemented it.

• Limiting a users use of disk space on Debian