Improve the Friendica backup script to handle database errors

beaglebone.txt

 editor /etc/cron.daily/backup
 #+END_SRC
 
-Enter the following
+Enter the following, replacing /myusername@mydomainname.com/ with your email address.
 
 #+BEGIN_SRC: bash
 #!/bin/sh
 
-# stop the web server to avoid any changes to the databases during backup
-service apache2 stop
+EMAIL=myusername@mydomainname.com
 
 MYSQL_PASSWORD=<mysql root password>
 umask 0077
 
+# stop the web server to avoid any changes to the databases during backup
+service apache2 stop
+
+# Save to a temporary file first so that it can be checked for non-zero size
+TEMPFILE=/tmp/friendicared.sql
+
 # Backup the database
-mysqldump --password=$MYSQL_PASSWORD friendica > /var/backups/friendica_daily.sql
+mysqldump --password=$MYSQL_PASSWORD friendica > $TEMPFILE
+FILESIZE=$(stat -c%s $TEMPFILE)
+if [ "$FILESIZE" -eq "0" ]; then
+    # restart the web server
+    service apache2 start
+
+	# Send a warning email
+	echo "Unable to create a backup of the Friendica database" | mail -s "Friendica backup" $EMAIL
+
+    exit 1
+fi
+
+chmod 600 $TEMPFILE
+mv $TEMPFILE /var/backups/friendica_daily.sql
 
 # Make the backup readable only by root
 chmod 600 /var/backups/friendica_daily.sql
 
 # Backup the database
-#mysqldump --password=$MYSQL_PASSWORD redmatrix > /var/backups/redmatrix_daily.sql
+#mysqldump --password=$MYSQL_PASSWORD redmatrix > $TEMPFILE
+
+FILESIZE=$(stat -c%s $TEMPFILE)
+if [ "$FILESIZE" -eq "0" ]; then
+    # restart the web server
+    service apache2 start
+
+	# Send a warning email
+	echo "Unable to create a backup of the Red Matrix database" | mail -s "Red Matrix backup" $EMAIL
+
+    exit 2
+fi
+
+chmod 600 $TEMPFILE
+mv $TEMPFILE /var/backups/redmatrix_daily.sql
 
 # Make the backup readable only by root
 #chmod 600 /var/backups/redmatrix_daily.sql
 
 # restart the web server
 service apache2 start
+
+exit 0
 #+END_SRC
 
 Save and exit.