solution 1

backup.sh

@@ -4,6 +4,12 @@
 set -eu
 IFS=$'\n\t'
 
+function _log {
+   logfile=$(basename $0).log
+   echo $(date) $@ >> $logfile
+}
+
+_log "starting"
 [ $UID -eq 0 ] || { echo "need to be root" ; exit 1 ; }
 
 if [ $# -lt 1 ] ; then
@@ -19,5 +25,8 @@ for dir in "$@" ; do
   test -d $dir || { echo $dir dont exists ; continue ; }
   dirname=$(basename $dir)
   tar -cpzf ${bdir}/${dirname}.tgz $dir
-  echo $? > /run/${dirname}.status
+  ret=$?
+  echo $ret > /run/${dirname}.status
+  _log backup of $dir done with code $ret
 done
+_log "done"