Warn about oflag=append without conv=notrunc.

ChangeLog

@@ -1,5 +1,8 @@
 2006-08-09  Paul Eggert  <eggert@cs.ucla.edu>
 
+	* src/dd.c (usage): Warn about oflag=append without conv=notrunc.
+	See Debian bug 373736.
+
 	* src/dircolors.hin: Add mlterm, rxvt-unicode; this fixes Debian
 	bug 317503.
 

doc/ChangeLog

@@ -1,3 +1,8 @@
+2006-08-09  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* coreutils.texi (dd invocation): Warn about oflag=append without
+	conv=notrunc.  See Debian bug 373736.
+
 2006-08-08  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* coreutils.texi (shuf invocation, Random sources): New sections.

doc/coreutils.texi

@@ -7302,6 +7302,9 @@ system.
 Write in append mode, so that even if some other process is writing to
 this file, every @command{dd} write will append to the current
 contents of the file.  This flag makes sense only for output.
+If you combine this flag with the @samp{of=@var{file}} operand,
+you should also specify @samp{conv=notrunc} unless you want the
+output file to be truncated before being appended to.
 
 @item direct
 @opindex direct

src/dd.c

@@ -458,7 +458,7 @@ Each CONV symbol may be:\n\
 \n\
 Each FLAG symbol may be:\n\
 \n\
-  append    append mode (makes sense only for output)\n\
+  append    append mode (makes sense only for output; conv=notrunc suggested)\n\
 "), stdout);
       if (O_DIRECT)
 	fputs (_("  direct    use direct I/O for data\n"), stdout);