Sun Microsystems unveiled NFS — the Network File System — in 1984, with the bold promise that remote disks would feel just like local ones. And they do, right up until the network hiccups, at which point every process touching an NFS mount freezes solid in uninterruptible sleep, immune to kill signals, and requiring a reboot to clear. This behavior was not a bug; it was a design choice, on the theory that the network would always come back. Unix veterans have a word for processes stuck in uninterruptible NFS sleep: “gone.” NFS version 4 arrived in 2000 with improvements. Sysadmins still flinch when they see df hanging.
