Using systemd in Fedora.....

To permanently enable a service:

#  systemctl enable ntpd.service

To start it:

# systemctl start ntpd.service

To view all services:

# systemctl

Finding Disk Hogs

Finding disk hogs

# du  /home/* | sort -n -r | less

Adding constraints to mysql tables

When we have content in a table that is dependant on another a constraint is required. With Mysql an InnoDB type is required otherwise the constraint is silently ignored. Consider a radios table, models table and a code_plugs table within the radio database.

The constraints would prevent a code_plug or models record being removed if a relative record in the radios table exists.


The create table entries would be:

CREATE TABLE `radios` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `status_id` int(4) NOT NULL DEFAULT '2',
  `model_id` int(4) NOT NULL,
  `serial_number` varchar(40) NOT NULL,
  `software_version` varchar(40) NOT NULL,
  `active` int(4) NOT NULL DEFAULT '1',
  `remarks` varchar(100) NOT NULL,
  `code_plugs_id` int(4) NOT NULL,
  `radio_id` int(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `serial_number` (`serial_number`),
  UNIQUE KEY `radio_id` (`radio_id`),
  CONSTRAINT `FK_code_plugs` FOREIGN KEY (`code_plugs_id`) REFERENCES `code_plugs` (`id`),
  CONSTRAINT `FK_models` FOREIGN KEY (`model_id`) REFERENCES `models` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1376 DEFAULT CHARSET=latin1;


CREATE TABLE `models` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `model` varchar(20) NOT NULL,
  `type` varchar(20) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=latin1;


CREATE TABLE `code_plugs` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `name` varchar(40) NOT NULL,
  `description` varchar(200) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1112 DEFAULT CHARSET=latin1;



A simple snippet of perl server side code to provide an xml response to a delete attempt would look like:


my $dbh = DBI->connect("dbi:mysql:radio",$dbuser,$dbpass,{RaiseError=>0});
my $id = param("id");
my $table = param("table");

my $rows = $dbh->do("DELETE FROM $table WHERE id = \'$id\';");
my $result;
if($dbh->errstr){
        $result = $dbh->errstr;
        $result =~ s/([\',\`])+//g;
}else{
        $result = $rows;
}

# results are 1 for success and 0E0 for failure
my $xml = '<?xml version="1.0"?>';
$xml .= "\n<options>\n";
$xml .= "<option result=\'$result\' />\n";
$xml .= "</options>";
print "$xml";

A simple javascript handler for the delete may look similar to :


function deleteID(id,table){
        if (confirm("Are you sure?")){
                var request;
                try{
                        request = new XMLHttpRequest();
                }catch(error){
                        try{
                                request = new ActiveXObject("Microsoft.XMLHTTP");
                        }catch(error){
                                return true;
                        }
                }
                request.open('GET', '/cgi-bin/deleteUsingID.pl?id=' + id + '&table=' + table,true);
                request.onreadystatechange = function(){
                        if(request.readyState == 4){
                                var xmlDoc = request.responseXML;
                                var options = xmlDoc.documentElement.getElementsByTagName("option");
                                for (var x = 0; x < options.length; x++){
                                        var result = (options[x].getAttribute("result"));
                                        if (result == '1'){
                                                var rid = 'row_' + id;
                                                var oTable = document.getElementById('content_table');
                                                var oTr = document.getElementById(rid);
                                                oTable.deleteRow(oTr.rowIndex);
                                        }else{
                                                alert(result);
                                        }
                                }
                        }
                }
                request.send(null);
        }
}

Removing files older than 5 minutes.

Quickly list files with time of last modification:
# ls -alt

If you need to remove any that have not been modified lately:

1. verify files that will be worked on by running with ls first
2. delete at will without warning

# find ./*.rrd -type f -mmin +5 -exec ls {} \;

# find ./*.rrd -type f -mmin +5 -exec rm {} \;

Changing Basic Authentication password for an apache web site.

1. Move to the folder where we retain the .htpasswd file (and hence want to protect)
2. Create or overwrite the .htpasswd file (in this case the user zephir exists already):
3. Reboot your browser and you should be challenged again for passwd

# htpasswd -c .htpasswd zephir
New password:
Re-type new password:
Adding password for user zephir

# apachectl restart or service httpd restart or systemctl restart httpd.service