I am using Ubuntu 12.04 and can't write to any file, even as root, or do any other operation that requires writing. Neither can any process that needs to write, so they're all failing.
df says I've got plenty of room:
Filesystem Size Used Avail Use% Mounted on /dev/xvda1 30G 14G 15G 48% / udev 984M 4.0K 984M 1% /dev tmpfs 399M 668K 399M 1% /run none 5.0M 0 5.0M 0% /run/lock none 997M 0 997M 0% /run/shm
All of the results I find for "can't write to disk" are about legitimately full disks. I don't even know where to start here. The problem appeared out of nowhere this morning.
PHP's last log entry is:
failed: No space left on device (28)
Unable to open (file) for writing
Other applications give similar errors.
After deleting ~1gb just to be sure, the problem remains. I've also rebooted.
df -i says
Filesystem Inodes IUsed IFree IUse% Mounted on /dev/xvda1 1966080 1966080 0 100% / udev 251890 378 251512 1% /dev tmpfs 255153 296 254857 1% /run none 255153 4 255149 1% /run/lock none 255153 1 255152 1% /run/shm