OCI- Unable to ssh to Instance with Error "Failed to remount '/' read-only: Device or resource busy"

Applies To:

Oracle Cloud Infrastructure

Linux OS 

Symptoms

It is not possible to connect to instance with ssh.

The console history for the instance shows the below error indicating the instance was previously powered off:

Reached target Final Step
         Starting Power-Off...
systemd-shutdown[9848]: Failed to remount '/' read-only: Device or resource busy
systemd-shutdown[1]: Failed to wait for process: Protocol error
connection1:0: detected conn error (1011)
reboot: Power down

Cause

In this case the issue is caused by the root filesystem ("/") directory becoming 100% full.

$ df -h /
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdaX             39G  38.6G     0 100% /

The /var/log/messages file shows: