Yesterday, I stumbled on a problem where rule MkDir1 tried and failed  to create a directory that already existed.&nbsp; This was in trying to  build a library with toolset gcc with os = CYGWIN after having built it  with other toolsets.&nbsp; I don't know what I did, but not I cannot  replicate the problem this morning.&nbsp; Must be change in the phase  of the moon.&nbsp; Nevertheless, would it hurt to add a defensive -p  flag to mkdir in tools/common.jam so that it won't fail when it  mistakenly tries to create a directory that already exists?&nbsp; I  recall someone complaining about this with Perforce jam.<br>  <br>  Regards,<br>  Mark<br>  <br>  <br>  RCS file: /cvsroot/boost/boost/tools/build/v2/tools/common.jam,v<br>  retrieving revision 1.45<br>  diff -u -r1.45 common.jam<br>  --- common.jam&nbsp;&nbsp;&nbsp; 15 Dec 2005 18:04:05 -0000&nbsp;&nbsp;&nbsp; 1.45<br>  +++ common.jam&nbsp;&nbsp;&nbsp; 16 Feb 2006 11:42:00 -0000<br>  @@ -528,7 +528,7 @@<br>  &nbsp;<br> 
 &nbsp;actions MkDir1<br>  &nbsp;{<br>  -&nbsp;&nbsp;&nbsp; mkdir "$(&lt;)"<br>  +&nbsp;&nbsp;&nbsp; mkdir -p "$(&lt;)"<br>  &nbsp;}<br>  &nbsp;<br>  &nbsp;actions piecemeal together existing Clean<br>  <br>  <br>