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OpenStack Grizzly Architecture

As OpenStack has continued to mature, it has become more complicated in some ways but radically simplified in others. From a deployers view, each service has become easier to deploy with more sensible defaults and the proliferations of cloud distributions. However, the architects view of OpenStack has actually gotten more complicated – new services have […]

RHEL 6 Security Guide

1. GRUB password

September 25th, 2014 | Category: Centos, RHCE | Leave a comment

RHEL 7 minimal install

1. during installation prompt, insert net.ifnames=0 to disable consistent network device naming

2. after first reboot of installation:

3. enable normal ethx interface name and disable ipv6 vi /etc/default/grub add net.ifnames=0,ipv6.disable=1 to GRUB_CMDLINE_LINUX line

grub2-mkconfig -o /boot/grub2/grub.cfg

4. disable UTC vi /etc/adjtime change UTC to LOCAl

5. disable selinux vi /etc/sysconfig/selinux SELINUX=disabled

6. disable […]

RHEL 7 RESCUE MODE

To list all currently loaded service units: systemctl list-units –type service

To list all installed service units: systemctl list-unit-files –type service

Lists currently loaded target units: systemctl list-units –type target

Changes the current target: systemctl isolate name.target

systemctl get-default

systemctl set-default name.target

systemctl rescue  (single user mode)

resetting root password: edit boot kernel line, insert […]

NIC Bonding on CentOS 6/7

Make sure not to use NetworkManager, using normal network

vi /etc/sysconfig/network-scripts/ifcfg-bond0 DEVICE=bond0 BOOTPROTO=none ONBOOT=yes IPADDR=192.168.1.27 NETMASK=255.255.255.0 GATEWAY=192.168.1.1 DNS1=8.8.8.8 USERCTL=no BONDING_OPTS=”mode=1 miimon=100″

vi /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 MASTER=bond0 SLAVE=yes USERCTL=no BOOTPROTO=none ONBOOT=yes sed  “s/eth0/eth1/g” ifcfg-eth0 > ifcfg-eth1

Install KVM on CentOS 7

yum -y install qemu-kvm qemu-img libvirt virt-install bridge-utils

lsmod | grep kvm

systemctl start libvirtd systemctl enable libvirtd

RHEL 7 notes To list all currently loaded service units: systemctl list-units –type service

To list all installed service units: systemctl list-unit-files –type service

Lists currently loaded target units: systemctl list-units –type target

Changes the current target: […]

Administration:Postfix Queue

Overview When is postfix used?

Postfix can be used for the following functionality:

Masquerading Shunting queue

The Postfix solution is not secured and hence should be used after the qmail server. Postfix can be put in front of qmail only on internal servers which are not exposed to direct hits from the Internet or LAN.

[…]

Postfix on CentOS 6.4

MAIL SERVERSETUP USING POSTFIX ON CENTOS 6.4

Part 1 MTA Postfix

Chapter 1 Email Service Chapter 2 Mail Transfer Agents Chapter 3 Installation and Startup Chapter 4 Postfix Configuration

Part 2 IMAP & POP3 Server

Chapter 5 IMAP and POP3 on Dovecot Chapter 6 MUA Configuration

Part 3 Postfix aliases & access control

Chapter […]

Qmail delivery problems

We’re a PA partner and have clustered Qmail with 4 servers + NFS storage. We’ve seen an issue where Qmail throws the following error:

failure: Sorry,_I_could_not_find_a_mail_exchanger_or_IP_address._(#5.4.4)/

This is a permanent error and means Qmail will not retry, the sender will receive an NDR (Non delivery reply / bounce back).

I’ve seen 3 causes so far […]

Configure Postfix on CentOS/RHEL 6/5

Postfix is fast and popular SMTP server widely used. The main job of postfix is to relay mail locally or to intended destination outside the network. Some of the most popular SMTP servers are Sendmail, Postfix and Qmail. By default Sendmail comes pre-installed with CentOS/RHEL 5. We will need to remove it and install Postfix. […]

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