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CentOS / RHEL 7 : Unable to start/enable iptables

When trying to start/enable the iptables daemon you receive the errors:

# systemctl enable iptables Failed to issue method call: Access denied # systemctl start iptables Failed to start iptables.service: Unit iptables.service failed to load: No such file or directory. Solution:

Starting with RHEL 7, firewalld is introduced and by default the iptables package is […]

CentOS / RHEL 7 : Never run the iptables service and FirewallD service at the same time!

By default, RHEL 7 uses the FirewallD service to provide network security. FirewallD must be stopped and disabled when using the iptables service:

# systemctl stop firewalld.service # systemctl disable firewalld.service # systemctl enable iptables.service # systemctl start iptables.service The iptables service is now provided by a separate package called iptables-services:

# yum info iptables-services […]

CentOS / RHEL 7 : How to open a port in the firewall with firewall-cmd?

Question: How to open a port in RHEL 7 using the firewall-cmd command?

Solution:

To begin with check the firewalld status using the systemctl command :

# systemctl status firewalld ? firewalld.service – firewalld – dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2016-10-29 21:47:04 IST; 1 weeks […]

CentOS / RHEL : Configure yum automatic updates with yum-cron service

yum-cron is an optional package starting from Red Hat Enterprise Linux 6, this is a plugin for yum. From man page of yum-cron :

yum-cron is a simple way to call yum commands from cron. It provides configuration to keep repository metadata up to date, and to check for, download, and apply updates. The yum-cron […]

CentOS / RHEL : How to install and start the Apache httpd service

Question: How to install Apache and configure Apache httpd to run as a service?

Answer:

Installing the Apache package

If you have the apache package downloaded, you can install it using rpm command as root user.

# rpm -ivh httpd If you have yum repository configured, use the recommended way of installing Apache httpd, i.e. […]

Why CentOS / RHEL 7 have many tmpfs (6 tmpfs filesystem), and what is their purpose

Question: Why CentOS 7 / RHEL 7 have many tmpfs (6 tmpfs filesystem), are these tmpfs mandatory for OS? What are the mount /run/user/1000, /run/user/0, /run/user/45, /sys/fs/cgroup for?

Answer:

If you run df -hP in RHEL 7 system you would find many tmpfs file systems mounted.

# df -hP Filesystem Size Used Avail Use% Mounted […]

CentOS / RHEL 7 : How to disable IPv6

Post describes procedure to disable IPv6 on CentOS/RHEL 7. There are 2 ways to do this : 1. Disable IPv6 in kernel module (requires reboot) 2. Disable IPv6 using sysctl settings (no reboot required)

To verify if IPv6 is enabled or not, execute :

# ifconfig -a | grep inet6 inet6 fe80::211:aff:fe6a:9de4 prefixlen 64 scopeid […]

RHEL 6 vs RHEL 7 Difference

Red Hat Enterprise Linux 7 is an major / drastic change to enterprise. To serve / meet today’s business critical application performance RHEL 7 is the best Operating system to use, very light weight and container based. In this article we are going to see RHEL 6 vs RHEL 7 Difference Between Previous and Newer […]

CentOS 7.3 under the Hadoop 2.7.2 cluster

CentOS 7.3 under the Hadoop 2.7.2 cluster

how to setup a Hadoop cluster on CentOS linux system. Before you read this article, I assume you already have all basic conceptions about Hadoop and Linux operating system.

mv ifcfg-eno16777736 ifcfg-eth0 vi /etc/udev/rules.d/90-eno-fix.rules # This file was automatically generated on systemd update SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:0c:29:9e:8f:95″, NAME=”eno16777736″

[…]

YumDownloader on CentOS 7 / RHEL 7

YumDownloader

yum install yum-utils yumdownloader bind-utils [root@lab4 ~]# yum install yum-utils Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: centos.shinjiru.com * extras: centos.netonboard.com * updates: centos.netonboard.com Resolving Dependencies –> Running transaction check —> Package yum-utils.noarch 0:1.1.31-40.el7 will be installed –> Processing Dependency: python-kitchen for package: yum-utils-1.1.31-40.el7.noarch –> Processing Dependency: libxml2-python for package: […]