This trick is for multiuser boxes to try and ammeleriate issues with people creating insecure temporary files (and to make it obvious which applications don't respect TMPDIR). The idea is to create a seperate directory for every user on the machine that's 700 to that user and point TMPDIR at it. I think that this idea could(/should?) be used by default by distributions.
mkdir /tmp/$USER 2>/dev/null if [ -O /tmp/$USER?; then
TMPDIR=/tmp/$USER
else
TMPDIR=$(mktemp -d /tmp/${USER}.XXXXXX)
fi
touch $TMPDIR/.bash.$$
TMP=$TMPDIR TEMP=$TMPDIR
export TMPDIR TMP TEMP
This means that it will remove the directory when the last shell is closed and there are no more files in the directory.
If users want scratch space to copy files between users etc, they can use /tmp directly as LFS suggests, however conformant programs should use /tmp/username or /tmp/username.uniqueid.
Ideally Linux could transparently produce a unique /tmp/ for each $USER on the system, but that would break LinuxStandardsBase compiliance and many applications.
One page links to PerUserTempDirs: