debian wheezy mounts /tmp as tmpfs by default

Recent changes in Debian sid indicate that /tmp is now mounted as tmpfs by default, being 20% of RAM available.

# man 5 rcS

       RAMTMP Make /tmp/ available as a ram file system (tmpfs).  Set to 'yes' to enable, to 'no' to disable.  It defaults to yes for new  installations  (wheezy  and later);  no  for  upgrades  from  earlier  releases,  which  do  not  contain RAMTMP in /etc/default/rcS.  The size of the tmpfs can be controlled using TMPFS_SIZE and TMP_SIZE in /etc/default/tmpfs.  However, /etc/default/tmpfs is deprecated and to override the defaults an entry  should  be  created  in /etc/fstab, for example:

              tmpfs     /tmp tmpfs     nodev,nosuid,size=20%,mode=1777    0    0

              Packages can not expect directories in /tmp to exist after boot.

Various applications put more into it, so it may result in problems.

The actual setting happens within /etc/default/rcS

RAMTMP=yes

is the key to be changed, if you do not want that behaviour. If the size needs to be adjusted, add a fstab entry instead.

Update 2012-12-30: This has been disabled by default. See follow-up here.