Redirect console output to another console.

First list out open console(pts).

[root@localhost ~]# ll /dev/pts/
total 0
crw--w----. 1 root tty  136, 0 Jan 22 21:09 0
crw--w----. 1 root tty  136, 1 Jan 22 08:53 1
crw--w----. 1 root tty  136, 2 Jan 22 21:04 2
crw--w----. 1 root tty 136, 3 Jan 22 21:04  3
c---------. 1 root root   5, 2 Jan 21 17:11 ptmx

From the output, we can see we have 4 pts terminal (0, 1, 2 and 3).

Here I am going to redirect output to “pts/3”.

[root@localhost ~]# /bin/bash > /dev/pts/3

 In the screenshot, we can see command output redirect to “pts3”

Linux Performance tuning

Using tuned profile we can tune. Tuned is a daemon that uses udev to monitor connected devices and statically and dynamically tunes system settings according to a selected profile. Tuned is distributed with a number of predefined profiles for common use cases like high throughput, low latency, or power save. It is possible to modify the rules defined for each profile and customize how to tune a particular device.

For tuning Linux we have various tools.

Using “tuned-adm”  command line tool for switching between different tuning profiles.

To list out all the available profile.

[root@feenixdv docker]# tuned-adm list
Available profiles:
- balanced                    - General non-specialized tuned profile
- desktop                     - Optmize for the desktop use-case
- latency-performance         - Optimize for deterministic performance at the cost of increased power consumption
- network-latency             - Optimize for deterministic performance at the cost of increased power consumption, focused on low latency network performance
- network-throughput          - Optimize for streaming network throughput.  Generally only necessary on older CPUs or 40G+ networks.
- powersave                   - Optimize for low power consumption
- throughput-performance      - Broadly applicable tuning that provides excellent performance across a variety of common server workloads.  This is the default profile for RHEL7.
- virtual-guest               - Optimize for running inside a virtual guest.
- virtual-host                - Optimize for running KVM guests
Current active profile: virtual-guest

[root@feenixdv ~]# ll /etc/tuned/
total 12
-rw-r--r--. 1 root root  14 Jan 21 22:29 active_profile
-rw-r--r--. 1 root root 779 Oct 17  2014 bootcmdline
-rw-r--r--. 1 root root 387 Mar  6  2015 tuned-main.conf
[root@feenixdv ~]# ll /usr/lib/tuned/
total 16
drwxr-xr-x. 2 root root    23 Jan 22  2019 balanced
drwxr-xr-x. 2 root root    23 Jan 22  2019 desktop
-rw-r--r--. 1 root root 12147 Oct 15  2014 functions
drwxr-xr-x. 2 root root    23 Jan 22  2019 latency-performance
drwxr-xr-x. 2 root root    23 Jan 22  2019 network-latency
drwxr-xr-x. 2 root root    23 Jan 22  2019 network-throughput
drwxr-xr-x. 2 root root    39 Jan 22  2019 powersave
-rw-r--r--. 1 root root   601 Oct 17  2014 recommend.conf
drwxr-xr-x. 2 root root    23 Jan 22  2019 throughput-performance
drwxr-xr-x. 2 root root    23 Jan 22  2019 virtual-guest
drwxr-xr-x. 2 root root    23 Jan 22  2019 virtual-host

And profile configuration file look like.

[root@feenixdv ~]# cat /usr/lib/tuned/balanced/tuned.conf
#
# tuned configuration
#
[cpu]
governor=conservative
energy_perf_bias=normal


timeout=10


radeon_powersave=auto

[disk]
# Comma separated list of devices, all devices if commented out.
# devices=sda
alpm=medium_power

To check the profile effect we have “tuna” GUI tool. You can install from ISO image.

Test case with “balanced”

Test case with “desktop”

Test case with “latency-performance”

Test case with “network-throughput”

Test case with “powersave”

Test case with “virtual-host”

Get tuned recommendation

To let tuned recommend you the best suitable profile for your system without changing any existing profiles and using the same logic as used during the installation, run the following command:

# tuned-adm recommend
virtual-guest

Create a custom tuned profile

# mkdir /etc/tuned/feenixdv
Create a new tuned.conf file for feenixdv, and insert new tuning info.
# vi /etc/tuned/feenixdv/tuned.conf
[main]
summary=This is a test tuned profile

[cpu]
force_latency=1

[vm]
transparent_hugepages=never

[sysctl]
kernel.sysrq=1
vm.nr_hugepages=4100
kernel.numa_balancing=0

[script]
script=/etc/tuned/feenixdv/myscript.sh

Here I have created a custom tuned profile which performs below list of functions

• limit C-state usage to C1
• disable transparent hugepages
• allocate 4100 2MB static hugepages
• disable automatic numa balancing
• run an arbitrary shell script

The content of an example myscript.sh script:

#!/bin/sh
OPERATION=$1
if [ $OPERATION -eq "start" ];
    then
            touch /tmp/$OPERATION
else
            touch /tmp/$OPERATION
fi

Provide executable permission to the tuned profile

# chmod +x /etc/tuned/feenixdv/tuned.conf

Next, enable the new profile

# tuned-adm profile feenixdv

Check the currently active profile

# tuned-adm active

GRUB 2 Command Shell

The GRUB 2 command shell is just as powerful as the shell in legacy GRUB. You can use it to discover boot images, kernels, and root filesystems. In fact, it gives you complete access to all file systems on the local machine regardless of permissions or other protections. Which some might consider a security hole, but you know the old Unix dictum: whoever has physical access to the machine owns it.

When you're at the grub> prompt, you have a lot of functionality similar to any command shell such as history and tab-completion. The grub rescue> mode is more limited, with no history and no tab-completion.

The first command you should run invokes the pager, for paging long command outputs:

grub> set pager=1

With ls command we can see available hard disk. In given output “hd0” is hard drive and “msdos1 to 3” are three partition.

Using ls command we can see content of particular partition. In given example we can see content of “msdos1” partition which is look like output of “/boot” partition because in the list we can see “grub2” directory and kernel images. Also initrd images.   

In this output “hd0,msdos3” is “root” partition and “hd0,msdos2” is most probe swap.

We can also use cat command to see any file content.

Booting From grub>

This is how to set the boot files and boot the system from the grub> prompt. We know from running the ls command that there is a Linux root filesystem on (hd0,1), and you can keep searching until you verify where /boot/grub is. Then run these commands, using your own root partition, kernel, and initrd image:

Booting From grub-rescue>

If you're in the GRUB rescue shell the commands are different, and you have to load the normal.mod andlinux.mod modules:

Configure High-Avaliablity Cluster on CentOS 7 / RHEL 7

Lab setup:-

Setup hostname on both node

[root@localhost ~]# hostnamectl set-hostname web1

Cross entry for each node and also check both node ping to each other with hostname.

In cluster setup we need some package with is presend in CD-ROM or ISO. Not in package folder(RHEL7). In “/mnt/addons/HighAvailability/” if CD-ROM mounted on “/mnt”.

We need to copy all the package(Package and HighAvailability) on one node and configure YUM using FTP so both node can install all package.

Going to install “iscsi-initiator-utils” on both node so node and mount shared storage “/dev/sdb1”.

Now going to discover storage from storage server.

We found one storage. Put storage details in “initiatorname.iscsi”.

Login into target Storage. Here we can see some issue in login. In this case just restart node and try after reboot.

Here you can see “/dev/sdb1” accessible from node. Something check from other node also.  

Through high availability here we are going to configure apache web server so first we need to install apache on both node.

[root@web1 ~]# yum install httpd -y

Update “httpd.conf” with below entry so it can we monitored. Put these entry in bottom of file.

Now mount storage on “/var/www/” and create one example page. Because SELinux enabled in so we need to restore same context for “html folder and index.html”.

After that allow on firewall and reload configuration.

Now configure HA cluster. For that we need to install some package.

Also add in firewall.

(On both node) To cross verify you can check “hacluster” user present or not.

If present then installation is ok. Otherwise you need to re-check all steps.

Now set password for hacluster user. Make sure password are same on both node.

Start “pcsd” services and enable it.

Authenticate all available node. In my lab setup we have only two node(web1 and web2).

setup cluster setting on both node(run only one node)

check status of cluster.

Check pacemaker status.

Now we are going to create three resources.

For system file(/dev/sdb1), for cluster VIP, apache config file and status.

All these resources are grouping with apache(–group apache).

Because the node level fencing configuration depends heavily on your environment, we will disable it for this tutorial.

Note: If you plan to use Pacemaker in a production environment, you should plan a STONITH implementation depending on your environment and keep it enabled.

Now you can see all resources are added and started.

[root@web1 ~]#

Migrate_Logical_Volume_To_Another_Disk

In this example, we have one Logical Volume(lv0) which belongs from vg0 on physical drive/partition “/dev/sdb1”.

Here we are going to migrate “lv0” to another disk “/dev/sdb2”.

First, we check particular Logical Volume present on which drive. Here we can see it on “/dev/sdb1”.   

Now add new disk “/dev/sdb2” in same Volume Group(vg0) with “vgextend” command.

Create mirroring of current Logical Volume to the new disk.

Now remove old disk “/dev/sdb1” and check all configuration on right disk and working properly. No need to un-mount during all activity.  

Check mount pint and data.

Everything is ok.

Restore deleted Logical Volume.

In this example, I have below configuration on the Linux box.

OS:- Linux rhel7 3.10.0-229.el7.x86_64

LVM details:-

•  lv0 on vg0
•  lv1 on vg1

Now I am going to create a scenario for practical means deleting one Logical Volume “lv0” and after that try to access or mount.

For each and every action on LVM, create a backup of the configuration file. Using these backups we can restore the configuration of the volume group. Is data also… depend on the situation.

Now going to restore from backup.

For that, we need to identify which backup file is used to restore Volume Group. For that, we use below process.

Now restore vg configuration with the backup file.

After restoring the lv in “inactive” state. We can see using “lvscan” command. To activate use “lvchange –ay /dev/vg0/lv0”.

Now you can see everything is OK.

Initialize hard drive without restarting in Linux

In this example you can see, we have only one hard disk interface “/dev/sda”.

Now I am going to add one extra hard disk(In my case I am using VMWare workstation)

After successfully added without a reboot, hard disk not initialize. We can see in the screenshot.

With below command, we can initialize hard disk without restart Linux box.

[root@rhel7 ~]# echo "- – -" > /sys/class/scsi_host/host0/scan

You can see all process in below screenshot.

Done.

Shell script for simple addition, subtraction and multiplication using case and function.

####################################################################

#!/bin/sh
#Script depend on three argument. first two are values and last one is operation
#Add Function for each operation
add() {
        result=`expr $1 + $2`;
        echo "Addition of $1 and $2 :- $result";
}

sub() {
        result=`expr $1 – $2`;
        echo "Subtraction of $1 and $2 :- $result";
}

mult() {
        result=`expr $1 \* $2`;
        echo "Multiply of $1 and $2 :- $result";
}

#Checking case with third value.
#Pass two argument $1 and $2 to function
case $3 in
add )
    add $1 $2 ;;
sub )
    sub $1 $2 ;;
mult )
    mult $1 $2 ;;
all )
    add $1 $2 ;
    sub $1 $2 ;
    mult $1 $2 ;;
esac

—————————————————-

Output look like:-

[root@rhel7 Script]# ./cash.sh 2 30 all
Addition of 2 and 30 :- 32
Subtraction of 2 and 30 :- -28
Multiply of 2 and 30 :- 60

####################################################################       

PXE Boot with kick-start configuration.

Configure PXE server.

[root@feenixdv_pix tftpboot]# cat /etc/redhat-release

CentOS Linux release 7.1.1503 (Core)

Step 1 :-

Install CentOS/RHEL on the virtual machine or any physical machine.

Step 2 :-

Install some prerequisite on PXE Server.

• vsftpd
• DHCP
• xinted
• tftp-server
• syslinux

Step 3 :-

To install these package configure local YUM repository with FTP.

YUM configuration:-

                1^st copy all data from CDROM to “/var/ftp/pub” location

                Next update yum repo file.

Note:- To use this setting “vsftpd” must be install first and start “vsftpd” service.

Step 4 :-

• Install all package after yum configuration.

   

   

   

   

  • yum install dhcp –y
  • yum install tftp-server
  • yum install syslinux

xinted automation installed with syslinux.

Step 5 :-

Now configure DHCP server.

Copy “dhcpd.conf” from from example file.

cat /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example > /etc/dhcp/dhcpd.conf

                update “/etc/dhcp/dhcpd.conf” according to network setting.

Step 6 :-

Now configure TFTP-SERVER server.

Then copy and create some configuration file for PXE installation.

Configure «default».

Step 7 :-

Now configure kick-start file.

                Copy this.

[root@feenixdv_pix tftpboot]# cp /root/anaconda-ks.cfg /var/ftp/pub/ks.cfg      

                Need to add url

Then copy “pxelinux.0” which was define in dhcpd.conf

cp /usr/share/syslinux/pxelinux.0 /var/lib/tftpboot/

Step 8 :-

Start all services and check on also.

[root@feenixdv_pix tftpboot]# systemctl restart vsftpd xinetd dhcpd

[root@feenixdv_pix tftpboot]# systemctl enable  vsftpd xinetd tftp.service dhcpd

Note:- Cross check firewall and selinux are disabled.

Now install new VM without in boobable media or source disk.

Some advance configuration in PXE for multiple version option.

For example we want to install RHEL5, RHEL6 and RHEL7 using PXE then first need to create same structure in “/var/ftp/pub” directory.

For RHEL5.

• Create directory “/var/ftp/pub/rhel5”
• Copy all package inside directory including ks.cfg, vmlinuz and initrd.img file.

Same for RHEL6 and RHEL7

Now update “/var/lib/tftpboot/pxelinux.cfg/default” and add below entry.

label RHEL_5
  menu label Install RedHat 5
  kernel rhel5/vmlinuz
  append initrd=rhel5/initrd.img ks=ftp://192.168.43.206/pub/rhel5/ks.cfg repo=ftp://192.168.43.206/pub/rhel5
  
label RHEL_6
  menu label Install RedHat 6
  kernel rhel6/vmlinuz
  append initrd=rhel6/initrd.img ks=ftp://192.168.43.206/pub/rhel6/ks.cfg repo=ftp://192.168.43.206/pub/rhe6
 
label RHEL_7
  menu label Install RedHat 7
  kernel rhel7/vmlinuz
  append initrd=rhel7/initrd.img ks=ftp://192.168.43.206/pub/rhel7/ks.cfg repo=ftp://192.168.43.206/pub/rhel7

Now again restart all services. After that we have below boot option on PXE boot.