/dev/sda8 on /tmp type tmpfs

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http://unix.stackexchange.com – I just went into fstab (Linux) and changed my line for /tmp (on which a specific ext4 partition was previously mounted) to tmpfs. This was clearly a bit silly, but I wasn't thinking. Anyway, I rebooted, and everything is working and all, but I'm confused. What does it mean that /dev/sda8 is mounted as tmpfs? If there were any files in /tmp, I can't access them any more, but I can create files in there. When I reboot, mounting as ext4 I can see that there were in fact files on the partition (that weren't visible when tmpfs was mounted). Is the device file meaningless in this context? (HowTos)