詳細はman 5 tmpfsして頂くとして、結果だけ。

[root@redmine ~]# uname -a
FreeBSD freebsd.babydaemons.homeip.net 8.2-RELEASE FreeBSD 8.2-RELEASE #0: Fri Feb 18 02:24:46 UTC 2011     root@almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386
[root@redmine ~]#
[root@freebsd ~]# dmesg | grep -i tmpfs
WARNING: TMPFS is considered to be a highly experimental feature in FreeBSD.
[root@freebsd ~]# grep tmpfs /etc/fstab
tmpfs                   /tmp            tmpfs   rw              0       0
[root@freebsd ~]# df -h /tmp
Filesystem    Size    Used   Avail Capacity  Mounted on
tmpfs         1.1G    5.7M    1.1G     0%    /tmp
[root@freebsd ~]# mount | grep /tmp
tmpfs on /tmp (tmpfs, local)
[root@freebsd ~]#

あのー、8.2に上がったのに"highly experimental"なんですか?? orz