/tmp and /usr/tmp

[Doug Gwyn]

/tmp is usually fast but rather small, /usr/tmp is better for large
temp files such as those used by rasterizers.  The library routines
described in TMPNAM(3S) use P_tmpdir defined in <stdio.h>, usually
/usr/tmp.  The tempnam() function is especially nice in that it lets
one change the temp file directory at runtime via an environment
variable $TMPDIR.  I encourage everyone to use tempnam().