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 […]

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RHEL 6 Security Guide

1. GRUB password i. run as root with /sbin/grub-md5-crypt to get a MD5 hash.  ii. add “password –md5 <password-hash>” below timeout line in /boot/grub/grub.conf  iii. prees p when access grub menu 2. Administrative Controls for Root Methods of Disabling the Root Account Method Description Effects Does Not Affect Changing the root shell. Edit the /etc/passwd file and change the shell from/bin/bash to /sbin/nologin. […]

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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 firewall systemctl stop […]

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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 […]

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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

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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: […]

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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. […]

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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 7 […]

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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 […]

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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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