Add a note about GNU tar's propensity to complain if a file changes

while tar is copying it.  This behavior is unhelpful when taking a base
backup.  Per gripe from Pallav Kalva back in April.

diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index e8f8b8a5813ad7c32dee47796550e46c9d06aec1..74f3add15c3d0b5749aabc08e7b92ce839152824 100644 (file)
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -1,5 +1,5 @@
 
 
  Backup and Restore
@@ -676,6 +676,15 @@ SELECT pg_stop_backup();
   
    
 
+   
+    Some versions of GNU tar consider it an error if a file
+    is changed while tar is copying it.  This case is normal,
+    and not an error, when taking a base backup of an active database.
+    Since ignoring all errors from tar would be unwise,
+    you should either manually inspect tar's messages or
+    else use a different backup tool that does not complain about this case.
+   
+
    
     It is not necessary to be very concerned about the amount of time elapsed
     between pg_start_backup and the start of the actual backup,