First, you need to access the server via SSH.
Most probably, your server has run out of free disk space. You can check the free space using the following command: df -h.
If there is no free space left, delete unnecessary files, outdated backup files, old logs and restart the server.
To explore the file system content, you can use the ncdu utility. Run it using the ncdu / command. After the disk analysis, you will get all the relevant information in a clear form:
