Add doc for spec. values of GMX_MAXBACKUP

Change-Id: Ibea096daa61e08e32f8dba05ba6afc5c7fbbb28c

diff --git a/manual/install.tex b/manual/install.tex
index 825e9dd8c5dbe6df138f17f63f3ec4cbe77344ee..08ad18e0692332728e76d73c8eeff2218011385e 100644 (file)
--- a/manual/install.tex
+++ b/manual/install.tex
@@ -165,7 +165,9 @@ you should consult your local documentation for details.
 \item   {\tt GMX_MAXBACKUP}: {\gromacs} automatically backs up old
         copies of files when trying to write a new file of the same
         name, and this variable controls the maximum number of
-        backups that will be made, default 99.
+        backups that will be made, default 99. If set to 0 it fails to
+        run if any output file already exists. And if set to -1 it
+        overwrites any output file without making a backup.
 \item   {\tt GMX_NO_QUOTES}: if this is explicitly set, no cool quotes
         will be printed at the end of a program.
 \item   {\tt GMX_SUPPRESS_DUMP}: prevent dumping of step files during