Redhat Enterprise Linux / CENTOS Support

Xen for CentOS7

Enable Repo :

#yum install centos-release-xen

#yum update

#yum install xen

verify kernel

#uname -r

#xl info

Setup Bridging :

ip route show | grep 'default' | awk '{print $5}'

nmcli con add type bridge con-name xenbr0 ifname xenbr0
nmcli con modify xenbr0 bridge.stp no
nmcli con modify xenbr0 bridge.hello-time 0

nmcli con show
nmcli con modify "System eth0" connection.master xenbr0 connection.slave-type bridge
systemctl restart network

RHEL8 - CENTOS8 Xen Dom0

Since KVM became default virtualization software from RHEL, after releasing of RHEL8 and CENTOS8 still XenSource RPMs are not available.

Fix for Zabbix4.0 installation on RHEL8 MariaDB10.3 error

There is problem on installing zabbix-server on RHEL8, while importing database schema error occurs.

Zabbix server version prior to 4.4 cannot work correctly with newer MariaDB versions out of the box.

Prior to MariaDB 10.2.26, 10.3.17, and 10.4.7, MariaDB didn't properly calculate the row sizes while executing DDL, so "unsafe" tables could be created, even with innodb_strict_mode=ON set. This was fixed by MDEV-19292.

shell> mysql -uroot -p<password>
mysql> set global innodb_strict_mode='OFF';

After importing Zabbix database schema

shell> mysql -uroot -p<password>
mysql> USE zabbix
mysql> alter table `host_inventory` modify `name` varchar(128) default '' not null, modify `alias` varchar(128) default '' not null, modify `os` varchar(128) default '' not null, modify `os_short` varchar(128) default '' not null;
mysql> set global innodb_strict_mode='ON';

MySQL Server is removed from Centos/RHEL 7 Repo

Big changes in open source world, i was just installing zabbix server and mysql database is required for zabbix. After installing Centos 7 from minimal install iso i didn't get mysql by "yum install mysql-server so i came to know about changes that "MySQL is no longer in CentOS’s repositories and MariaDB has become the default database" who knows mariaDB ??

any way you can still install mysql by installing official mysql community Yum's Repo file for "yum install mysql-server"

Method : Download and install from this url

http://repo.mysql.com/mysql-community-release-el7-5.noarch.rpm

or simply rpm -ivh http://repo.mysql.com/mysql-community-release-el7-5.noarch.rpm

Gnu Sed Utility

Example :

removing # (commented Lines) from a file

sed '/ *#/d; /^ *$/d' /sourcefile >/destfile

Cactiez Backup Restore

Restoring Cacti Backup from old server in easy steps .

Default Backup directory : /var/www/backups

tar -xzvf /var/www/backups/cacti-backup-year-month-Date.tar.gz

Data Base Import :

mysql cacti < /var/www/html/cacti-backup.sql
mysql syslog < /var/www/html/syslog.sql

Restart All CactiEz Services

Install centos6 from internet (netinstall)

Installing Centos6 / Rhel 6 From Network (Internet) :

We need ISO image from this links : image size is only 170 MB.

32 bit: http://linux.mirrors.es.net/centos/6.0/isos/i386/CentOS-6.0-i386-netinstall.iso
64 bit: http://linux.mirrors.es.net/centos/6.0/isos/x86_64/CentOS-6.0-x86_64-netinstall.iso

Burn Iso image to cd by your favorite image burner..

boot from cdrom and follow the instructions.

At Installation method menu select URL

configure ip address to access internet.

input this url for netinstall :

http://mirror.centos.org/centos/6/os/i386

Now install as normal installation.

how to make routing in redhat 6

In RHEL6 / CENTOS6 /FEDORA you can add static roure by applying route add command. but it is a temporary route.

for static roure, you can do it by modifying route-eth files..

ath of file : /etc/sysconfig/network-scripts

modify route-eth0 or route-eth1 file on which Ethernet interface you want to add route,

if file is not present create a file

# vi /etc/sysconfig/network-scripts/route-eth0

add following lines :

ADDRESS0=X.X.X.X
NETMASK0=X.X.X.X
GATEWAY0=X.X.X.X

example :

ADDRESS0=192.168.10.0       Destination Network Address

NETMASK0=255.255.255.0      Destination Network Subnet mask

GATEWAY0=192.168.2.1        Gateway address for that network

IF YOU WANT MORE ROUTES TO BE ADDED, APPLY 1,2,3, ETC.

CentOS 6 Download Link

CentOS is a Fork / Clone of RHEL ( RedHat Enterprise Linux), Basically RHEL is a Linux Distribution Under GNU GPL License but not free. So CentOS is a project to provide Enterprise Linux Free of cost. There is no more technical difference between RHEL and CentOS. If you want to install RHEL, you must create account to download RHEL ISO file and it is evolution version so we highly recomend that you first try CentOS which is free and opensource..

These are the links for to download CENTOS 6 ISO File, Download it and Burn it on CD / DVD with your favourite Burning program.

CentOS 32 bit DVD ISO File

CentOS 32 bit Live CD ISO File

CentOS 32 bit Live DVD ISO File

CentOS 64 bit DVD -1 ISO File

CentOS 64 bit DVD -2 ISO File

CentOS 64 bit Live CD ISO File

CentOS 64 bit Live DVD ISO File

How-to-Configure Network in RHEL6 Centos6

In RHEL6 and CentOS6 there is not System-Config-Network Script available which was very handy and useful.. Its good thing that now your require Basic Knowledge of Linux config File.. which is a best practice for Real Unix / Linux Admins.

Basically /etc contains Config files for system.
for network there is a directory called /etc/sysconfig/network-script/

There are ifcfg-eth(number) file for every Ethernet interface e.g ifcfg-eth0 for Ethernet 0, ifcfg-eth1 for Ethernet 1

Now create a file or Edit a file called /etc/sysconfig/network-script/ifcfg-eth0

------------------------------------------------------------------------------------------------------------

DEVICE=eth0

IPADDR=192.168.0.1
NETMASK=255.255.255.0
NETWORK=192.168.0.0
BROADCAST=192.168.0.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no

------------------------------------------------------------------------------------------------------------

These are the values which you can configure in config file :

DEVICE=devicename, where devicename is the name of the physical network device.

IPADDR=ipaddr, where ipaddr is the IP address.

NETMASK=netmask, where netmask is the netmask IP value.

NETWORK=network, where network is the network IP address.

BROADCAST=broadcast, where broadcast is the broadcast IP address.

ONBOOT=answer, where answer is yes or no. Do the interface need to be active or inactive at boot time.

BOOTPROTO=proto, where proto is one of the following :

none - No boot-time protocol should be used.

bootp - The bootp now pump protocol should be used.

dhcp - The dhcp protocol should be used.

USERCTL=answer, where answer is one of the following:

yes - Non-root users are allowed to control this device.

no - Only the super-user root is allowed to control this device.

no system-config-network in rhel6 centos6

Terminal Based Gui utility System-config-network for configuring ip address, subnet mask, gateway, DNS for each Network Connection is no longer supported in RHEL6.

There are so many changes in RHEL6 and its variants like CentOS6 and other.

It was really a very user friendly utility specially for newbies and Linux begginers...

Please Read our next post for configuring network interfaces in old classic Unix / Linux style... directly modifying config file.

Syslog NG- Best Open source Syslog Server

xen-hvm-qemu

Xen-HVM

The Xen virtual machine monitor can run in HVM (hardware virtual machine) mode, using Intel VT-x or AMD-V hardware x86 virtualization extensions. This means that instead of paravirtualized devices, a real set of virtual hardware is exposed to the domU to use real device drivers to talk to.
QEMU includes several components: CPU emulators, emulated devices, generic devices, machine descriptions, user interface, and a debugger. The emulated devices and generic devices in QEMU make up its device models for I/O virtualization.
Xen-HVM has device emulation based on the QEMU project to provide I/O virtualization to the VMs. Hardware is emulated via a patched QEMU "device model" (qemu-dm) daemon running as a backend in dom0. This means that the virtualized machines see as hardware: a PIIX3 IDE (with some rudimentary PIIX4 capabilities), Cirrus Logic or plain VGA emulated video, RTL8139 or NE2000 network emulation, PAE, and somewhat limited ACPI and APIC support and no SCSI emulation.

CEntOS6 will release soon

There are only 2-3 dys remaining for Official CentOS version 6 release.. QA and all process are Tested now the will put Centos6 ISO file within some days.. We will update download link as soon as possible

Mount NTFS Hdd in CetnOS/ RHEL

CEntOS - 5 and RHEL-5 is not supporting mounting of NTFS partition, fix harddisk, removable usb harddisk with NTFS partition

some packages need to be installed on it to make NTFS mountable

which are fuse and fuse-ntfs-3g

first of all apply this command to install these packages :

# yum install fuse fuse-ntfs-3g

after installing get the device name of connected hdd which we are going to mount

fdisk -l

in this example external hdd with ntfs partition is sdb2

make a directory / folder to mount hdd

# mkdir /media/hdd

mount sdb2 by this command

mount /dev/sdb2 /media/hdd

and you are doneeeeeeeee......

now you can access the data from ntfs mounted partition

DNS server types

master: Stores original and authoritative zone records for a namespace, and answers queries about the namespace from other nameservers.
slave: Answers queries from other nameservers concerning namespaces for which it is considered an authority. However, slave nameservers get their namespace information from master nameservers.
caching-only: Offers name-to-IP resolution services, but is not authoritative for any zones. Answers for all resolutions are cached in memory for a fixed period of time, which is specified by the retrieved zone record.
forwarding: Forwards requests to a specific list of nameservers for name resolution. If none of the specified nameservers can perform the resolution, the resolution fails.

A nameserver may be one or more of these types. For example, a nameserver can be a master for some zones, a slave for others, and only offer forwarding resolutions for others.

system-config-network

system-config-network tool is very helpful for configuring network address.

With root access you can start this command based gui tool by applying this command.

[root@vps ~]# system-config-network

how to make a iso image from cdrom under CentOS/RHEL

In Virtualization everything is virtual, so if you are planning for a virtual machine installation. it will be easy for you to make a iso image from cd/dvd and mount it as a virtual cdrom..

in linux dd command can do this things ..

This is an Example :

[root@vps ~]# dd if=/dev/cdrom of=xp.iso

dd command will make a xp.iso image file from physical cdrom..

Nic emulation supported by xen

The following emulated network interface cards are available for Xen HVM guests in Xen 3.4:

e100
e1000
rtl8139
ne2k_pci
pcnet

Emulation is done by Qemu-dm running for each Xen HVM guest. Intel e1000 is known to be the best performing emulated NIC. Even faster is to use PV-on-HVM drivers, which totally bypasses emulation.