$ mount | grep pipefs
rpc_pipefs on /run/rpc_pipefs type rpc_pipefs (rw)

$ fuser -vm /var/lib/nfs/rpc_pipefs
                     USER        PID ACCESS COMMAND
/var/lib/nfs/rpc_pipefs:
                     root     kernel mount /
                     shao       5453 .r.e. gnome-session
                     shao       5498 .rce. dbus-launch
                     shao       5499 .rce. dbus-daemon
                     shao       5501 .rce. gvfsd
                     shao       5503 .rce. gvfs-fuse-daemo
                     shao       5514 .rce. gconfd-2
                     shao       5519 .r.e. gnome-settings-
                     shao       5530 .r.e. compiz
                     shao       5542 .rce. pulseaudio
                     shao       5544 .rce. gvfsd-metadata
                     shao       5550 .rce. gconf-helper
                     shao       5551 .r.e. gnome-fallback-
                     shao       5552 .r.e. vino-server
                     shao       5553 .r.e. nm-applet
                     shao       5558 .rce. gvfs-gdu-volume
                     shao       5560 .r.e. polkit-gnome-au
                     shao       5569 .rce. mission-control
                     shao       5571 .r.e. nautilus
                     shao       5574 .r.e. bluetooth-apple
                     shao       5580 .rce. goa-daemon
                     shao       5583 .rce. gvfs-gphoto2-vo
                     shao       5591 .rce. gvfs-afc-volume
                     shao       5605 Fr.e. dropbox
                     shao       5611 .rce. gvfsd-trash
                     shao       5616 .rce. gvfsd-burn
                     shao       5695 .rce. dconf-service
                     shao       5699 .rce. bamfdaemon
                     shao       5715 .r.e. gdu-notificatio
                     shao       5727 .rce. notify-osd
                     shao       5749 .rce. unity-panel-ser
                     shao       5755 .rce. hud-service
                     shao       5768 .r.e. sh
                     shao       5769 .r.e. gtk-window-deco
                     shao       5771 .rce. indicator-appli
                     shao       5773 .rce. indicator-datet
                     shao       5776 .rce. indicator-messa
                     shao       5778 .rce. indicator-sound
                     shao       5782 .rce. indicator-sessi
                     shao       5786 frce. indicator-print
                     shao       5813 .rce. geoclue-master
                     shao       5815 .rce. ubuntu-geoip-pr
                     shao       5821 .r.e. telepathy-indic
                     shao       5827 .r.e. gnome-screensav
                     shao       5828 .r.e. zeitgeist-datah
                     shao       5834 .rce. zeitgeist-daemo
                     shao       5842 .rce. zeitgeist-fts
                     shao       5850 .rce. cat
                     shao       5852 .r.e. gnome-terminal
                     shao       5859 frce. unity-applicati
                     shao       5861 .rce. unity-files-dae
                     shao       5863 .rce. unity-music-dae
                     shao       5865 .rce. unity-lens-vide
                     shao       5895 .rce. unity-musicstor
                     shao       5896 .r.e. bash
                     shao       5981 .rce. unity-scope-vid
                     shao       6004 Frce. ubuntuone-syncd
                     shao       6136 Fr.e. firefox
                     shao       6158 .rce. at-spi-bus-laun
                     shao       6169 Fr.e. update-notifier
                     shao       6208 .r.e. plugin-containe
                     shao       6261 .r.e. plugin-containe
                     shao       6267 Frce. GoogleTalkPlugi
                     shao       6299 .r.e. deja-dup-monito