Configure CentOS to Sync with NTP Time Servers

 CentOS 7 / RHEL 7, Clusterweb, ClusterWeb, Leitura Recomendada, Linux, Profissional de TI  Comentários desativados em Configure CentOS to Sync with NTP Time Servers
ago 012019
 

Over the years, We’ve encountered many questions on how to correctly configure our Linux hosts to sync time to our enterprise NTP Servers.

So, We thought why not create an article that outlines in the simplest form possible the correct way to configure the NTP Client to synchronize with NTP Servers.

Sync CentOS with NTP Time Servers

First of all, we need to install the ntpd and ntpdate clients on our Linux host. I’m using CentOS, but it’s the same in Ubuntu and so forth.

# yum install ntp ntpdate
# systemctl start ntpd
# systemctl enable ntpd
# systemctl status ntpd

Now let’s run the following command to configure the NTP Servers.

# ntpdate -u -s 0.centos.pool.ntp.org 1.centos.pool.ntp.org 2.centos.pool.ntp.org

What we’re doing is telling the ntpdate to use an unprivileged port for outgoing packets with the -u switch and to write logging output to the system syslog facility using the -s switch.

Next let’s restart the ntpd daemon.

# systemctl restart ntpd

Now let’s check if NTP synchronization is enabled and running.

# timedatectl

And for the last, we will set the hardware clock to the current system time using the -w switch.

# hwclock -w

Congratulations! You’ve now successfully set your NTP client on CentOS.

How To Configure Bind as a Caching or Forwarding DNS Server

 CentOS 7 / RHEL 7, Clusterweb, ClusterWeb, Debian, Dns, Leitura Recomendada, Linux, Profissional de TI, Redes, Segurança, Ubuntu  Comentários desativados em How To Configure Bind as a Caching or Forwarding DNS Server
set 272018
 

Introduction

DNS, or the Domain Name System, is often a difficult component to get right when learning how to configure websites and servers. While most people will probably choose to use the DNS servers provided by their hosting company or their domain registrar, there are some advantages to creating your own DNS servers.

In this guide, we will discuss how to install and configure the Bind9 DNS server as a caching or forwarding DNS server on Ubuntu 14.04 machines. These two configurations both have advantages when serving networks of machines.

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Install NTOP on Debian and Configure to Use NetFlow on Mikrotik RouterOS

 Apache2, Clusterweb, Leitura Recomendada, Linux, Mikrotik, Profissional de TI, Redes, Segurança  Comentários desativados em Install NTOP on Debian and Configure to Use NetFlow on Mikrotik RouterOS
jun 182014
 

Ntop is a network monitoring tool similar to Unix top, which shows network traffic usage. It can act as a NetFlow collector for flows generated by routers such as Cisco or Mikrotik. NetFlow is an industry standard for flow-based traffic monitoring.

We will install and configure Ntop to collect flows generated by Mikrotik router. Note: “Ntop” != “NtopNG”.

Install Pre-required Software

We’re using Debian Wheezy:

$ uname -rv
3.2.0-4-686-pae #1 SMP Debian 3.2.51-1

Update the system first:

# apt-get update && apt-get upgrade -uV

Install required software:

# apt-get install libtool automake autoconf make build-essential python-dev subversion

Install external tools and libraries required by ntop:

# apt-get install libpcap-dev libgdbm-dev zlib1g-dev libgeoip-dev libgraphviz-dev \
> graphviz rrdtool librrd-dev

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RedHat / CentOS Install and Configure Cacti Network Graphing Tool

 Leitura Recomendada, Linux, Redes  Comentários desativados em RedHat / CentOS Install and Configure Cacti Network Graphing Tool
jun 192013
 

Cacti is a network graphing tool similar to MRTG. How do I install and configure common options to collect SNMP data and various other data (such as system load, network link status, hard disk space, logged in users etc) into an RRD?

From the official project site:

Cacti is a complete frontend to RRDTool, it stores all of the necessary information to create graphs and populate them with data in a MySQL database. The frontend is completely PHP driven. Along with being able to maintain Graphs, Data Sources, and Round Robin Archives in a database, cacti handles the data gathering. There is also SNMP support for those used to creating traffic graphs with MRTG.

Required software(s)

You need to install the following software on RHEL / Fedora / CentOS Linux:

  1. MySQL Server : Store cacti data.
  2. NET-SNMP server – SNMP (Simple Network Management Protocol) is a protocol used for network management.
  3. PHP with net-snmp module – Access SNMP data using PHP.
  4. Apache / lighttpd / ngnix webserver : Web server to display graphs created with PHP and RRDTOOL.

Install the software

First, login as root user and type the following command to install mysql, apache and php:
# yum install mysql-server mysql php-mysql php-pear php-common php-gd php-devel php php-mbstring php-cli php-snmp php-pear-Net-SMTP php-mysql httpd

Configure MySQL server

First, set root password:
# mysqladmin -u root password NEWPASSWORD

Create cacti MySQL database

Create a database called cacti, enter:
# mysql -u root -p -e 'create database cacti'
Create a user called cacti with a password called zYn95ph43zYtq, enter:
# mysql -u root -p

mysql> GRANT ALL ON cacti.* TO cacti@localhost IDENTIFIED BY 'zYn95ph43zYtq';
mysql> FLUSH privileges;
mysql> \q

Install snmpd

Type the following command to install net-snmpd
# yum install net-snmp-utils php-snmp net-snmp-libs
Configure snmpd, open /etc/snmp/snmpd.conf
# vi /etc/snmp/snmpd.conf
Append / modify it as follows (see snmpd.conf man page for details):

com2sec local     localhost           public
group MyRWGroup v1         local
group MyRWGroup v2c        local
group MyRWGroup usm        local
view all    included  .1                               80
access MyRWGroup ""      any       noauth    exact  all    all    none
syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root <root@localhost> (configure /etc/snmp/snmp.local.conf)
pass .1.3.6.1.4.1.4413.4.1 /usr/bin/ucd5820stat

Save and close the file. Turn on snmpd service:
# /etc/init.d/snmpd start
# chkconfig snmpd on

Make sure you are getting information from snmpd:
# snmpwalk -v 1 -c public localhost IP-MIB::ipAdEntIfIndex
Sample ouptut:

IP-MIB::ipAdEntIfIndex.10.10.29.68 = INTEGER: 2
IP-MIB::ipAdEntIfIndex.67.yy.zz.eee = INTEGER: 3
IP-MIB::ipAdEntIfIndex.127.0.0.1 = INTEGER: 1

Install cacti

First, make sure EPEL repo is enabled. Type the following command to install cacti:
# yum install cacti

Install cacti tables

Type the following command to find out cacti.sql path:
# rpm -ql cacti | grep cacti.sql
Sample output:

/usr/share/doc/cacti-0.8.7d/cacti.sql

Type the following command to install cacti tables (you need to type the cacti user password):
# mysql -u cacti -p cacti < /usr/share/doc/cacti-0.8.7d/cacti.sql

Configure cacti

Open /etc/cacti/db.php file, enter:
# vi /etc/cacti/db.php
Make changes as follows:

 
/* make sure these values refect your actual database/host/user/password */
$database_type = "mysql";
$database_default = "cacti";
$database_hostname = "localhost";
$database_username = "cacti";
$database_password = "zYn95ph43zYtq";
$database_port = "3306";

Save and close the file.

Configure httpd

Open /etc/httpd/conf.d/cacti.conf file, enter:
# vi /etc/httpd/conf.d/cacti.conf
You need to update allow from line. Either set to ALL or your LAN subnet to allow access to cacti:

 
#
# Cacti: An rrd based graphing tool
#
Alias /cacti    /usr/share/cacti

<Directory /usr/share/cacti/>
        Order Deny,Allow
        Deny from all
        Allow from 10.0.0.0/8
</Directory>

Another option is create /usr/share/cacti/.htaccess file and password protect the directory. Finally, restart httpd:
# service httpd restart

Setup cacti cronjob

Open /etc/cron.d/cacti file, enter:
# vi /etc/cron.d/cacti
Uncomment the line:

*/5 * * * *     cacti   /usr/bin/php /usr/share/cacti/poller.php > /dev/null 2>&1

Save and close the file.

Run cacti installer

Now cacti is ready to install. Fire a webbrowser and type the url:
http://your.example.com/cacti/
OR
http://your.server.ip.address/cacti/
Just follow on screen instructions. The default username and password for cacti is admin / admin. Upon first login, you will be force to change the default password.

How do I configure SNMP data collection?

SNMP can be used to monitor server traffic. Once installed login to cacti.
=> Click on Devices

=> Select Localhost

=> Make sure SNMP options are selected as follows:

Fig.01: SNMP configuration

Fig.01: SNMP configuration

Finally, click on Save button.

How do I create SNMP graphs?

Click on “Create Graphs for this Host” link on top right side.

Select SNMP – Interface Statistics

Select a graph type (such as In/Out bytes with total bandwidth)

Finally, click on Create button.

How do I view graphs?

To view graphs click on Graphs tab. Here is sample graph from one my own box:

 

Fig.02: Cacti in Action - Memory, CPU and Network Usage

Fig.02: Cacti in Action – Memory, CPU and Network Usage
(Fig.02: Cacti in action)

 

Fig.03: Cacti in Action Disk, Load average and User stats

Fig.03: Cacti in Action Disk, Load average and User stats

Further readings: