Reference
when executing df -hl
shows /tmp is mounted on overflow :
overflow 1.0M 1.0M 0 100% /tmp
If your “/tmp” mount on a linux filesystem is mounted as overflow (often sized at 1MB), this is likely due to you not specifying “/tmp” as its own partition and your root filesystem filled up and “/tmp” was remounted as a fallback. To fix this after you’ve cleared space, just unmount the fallback and it should remount at its original point:
sudo umount overflow
If you get device is busy
you can use sudo umount -l overflow