Disk Has Space But Can't Create Files? (Linux Inode Exhaustion)

One of the most confusing Linux errors I've debugged: a production server reporting "No space left on device" while df -h clearly showed 50GB free. I lost an hour to it the first time. Here's what was actually going on. I turned scenarios like this into an interactive practice tool at scenar.site - you debug simulated servers by talking to an AI interviewer. More at the end. The Setup I was on-call for a logging pipeline. Rsyslog kept crashing, and the logs were full of this: rsyslog[8421]: cannot create '/var/log/syslog.1': No space left on device systemd[1]: rsyslog.service: Main process exited, code=exited, status=1/FAILURE First instinct: the disk is full. Easy fix, right? The Investigation $ df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 100G 45G 50G 48% / /dev/sda2 20G 8.0G 11G 42% /var/log Wait, what? 50GB free on root, 11GB free on /var/log. The disk isn't full. But the error clearly said "No space left on device". So what's going on? This is the moment where a lot