Convert OpenSSH RSA or DSA key to PEM format

RSA to PEM

First create an RSA key using OpenSSH tools:

$ ssh-keygen -t rsa

Then converted it to PEM format:

$ openssl rsa -in ~/.ssh/id_rsa -outform pem > id_rsa.pem

DSA to PEM

First create an DSA key using OpenSSH tools:

$ ssh-keygen -t dsa

Then converted it to PEM format:

$ openssl dsa -in ~/.ssh/id_dsa -outform pem > id_dsa.pem

kill process based on username and logout users

To kill all process of logged in user and logout

pkill -KILL -u username

Know Number of Logged in User in FreeRadius from Shell

This is a very useful perl script that i created to know how many user are logged in on FreeRadius from the UNIX/Linux shell or command line.

It’s for FreeRadius with MySQL and I think it is usefull for other radiuses as well.
Below is the full code.

#!/usr/bin/perl -w

use DBI;

my $db = 'radius';
my $db_host = 'localhost';
my $db_username = 'username';
my $db_password = 'password';
my $dbh = DBI->connect("dbi:mysql:database=$db;host=$db_host:port number;user=$db_username;password=$db_password") or die "Couldn't connect to database: $DBI::errstr\n";

my $sql = qq{SELECT DISTINCT UserName,AcctStartTime,FramedIPAddress,CallingStationId FROM radacct WHERE AcctStopTime = '0000-00-00 00:00:00' AND NASIPAddress = '192.168.254.2' GROUP BY UserName};

$sth = $dbh->prepare($sql) or die "Couldn't prepare query '$sql': $DBI::errstr\n";

$sth->execute() or die "Couldn't execute query '$sql': $DBI::errstr\n";

print $sth->rows();

$sth->finish();

$dbh->disconnect();

exit;

Note:
change the username and password to actual username and password of a MySQL database, and NASIPAddress.

FreeBSD VLANs Configuration using ifconfig command

To create a new VLAN interface, enter:
# ifconfig {vlan-name} create

To associate the VLAN interface with a physical interface and assign a VLAN ID, IP address, and netmask:
# ifconfig {vlan-name} {ip-address} netmask {subnet-mask} vlan {vlan-id} vlandev {physical-interface}

The following examples, all packets will be marked on egress with 802.1Q VLAN tags, specifying a VLAN ID of 500:
# ifconfig vlan500 10.0.0.1 netmask 255.255.255.0 vlan500 vlandev em0

To remove a VLAN interface, enter:
# ifconfig {vlan-name} destroy

To make configuration persistence, open /etc/rc.conf:
# vi /etc/rc.conf

Append / modify as follows:
cloned_interfaces=“vlan500 vlan600”
ifconfig_vlan500="inet x.x.x.x netmask y.y.y.y vlan 500 vlandev em0"
ifconfig_vlan600="inet x.x.x.x netmask y.y.y.y vlan 600 vlandev em0"

Static ARP entry

arp -s ip_address ethernert_address

example:

arp -s 192.168.69.126 00:1f:f3:52:20:ed

arp -S ip_address ethernert_address
- Is just like -s except any existing ARP entry for this host will be deleted first.

example:

arp -S 192.168.69.126 00:1f:f3:52:20:ed