About Ubuntu 18.04

About Ubuntu 18.04

We are going to see about Ubuntu 18.04 Operating system, which is going to release on 26th April 2018.

Features of Ubuntu 18.04:

GNOME 3.28 Desktop

Ubuntu 18.04 going to give us a new experience.

Kernel 4.15

Ubuntu has scheduled to come up with new kernel version for every 6 months. Now Kernel 14.5 going to give more power to Ubuntu.

Xorg

Xorg is the default one for Ubuntu and from next release, TLS will come with both traditional Xorg graphics and Way-land based stack. It will give better performance to software like Skype, hangout and it will recover better from the shell crashes.

Minimal installation method

From ubuntu 18.04 we have an option to install with minimal packages and it will give us a desktop environment.Note: This is not a replacement for existing Ubuntu minimal ISO.

Ubuntu will collect data

As per Ubuntu announcement, canonical will collect some user data like system configuration and installed packages and this option will be available in the installer.

New installer

Subiquity will be the default one in an upcoming release and this will give new look to server installation.

Color emojis

Its important in messaging and communication. It will display colorful emojis in all the apps.

Faster boot time

Using systemd it will speed up the booting time.

zstd compression algorithm

Using facebook’s zstd compression algorithm it speeds up the Ubuntu installation process.

refrence: Ubuntu wiki

Logrotate in Linux

Will see how to configure/ use logrotate in Linux

to compress, move, delete or mail log files at the periodic time. By doing this will keep away the filesystem from the filesystem full issue.

Setting up and Manage logrotate in Linux:

In Linux/ Unix, environment /var/log is most important directory and it keeps all the activities as a log.

System administrators will use the logs to analyze any issue’s.

/var/log keeps lots of log files and here is the list.

[root@localhost ~]# ls /var/log
anaconda boot.log cron dmesg.old lastlog messages rhsm spooler tuned wtmp
audit btmp dmesg firewalld maillog ppp secure tallylog vmware-vmsvc.log

Installing logrotate:

Here I am going to use the yum package manager to install the logrotate.

[root@localhost ~]# yum install logrotate
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Package logrotate-3.8.6-12.el7.x86_64 already installed and latest version
Nothing to do

look likes the package is already installed on my machine.

/etc/logrotate.conf is an important configuration file which contains all the configuration of log rotation and “include /etc/logrotate.d ” this line should be uncommented.

We have plenty of option in logrotate and below is that.

Will create /etc/logrotate.d/apache2.conf file and insert below content.

/var/log/apache/* {
weekly
rotate 5
size 25M
compress
delaycompress
}

Daily, Weekly, Monthly:  Based on this input the tool will rotate the logs.

rotate 5: This will keep the only 5 files and the old files will be removed.

size 25: log file minimum size for log rotation.

Compress & Delaycompress:  These are used to say that all are already rotated logs.

Now will do s test using the below command

[root@localhost ~]# logrotate -d /etc/logrotate.d/apache2.conf

 

 

Reference: Tecmint

About Veritas Cluster Server

About Veritas Cluster Server

We will start to learn About Veritas Cluster Server and how to manage it, in this post.

VCS is Symantec product and it connects single, multiple nodes under a framework to provide increased availability.

All the nodes will run using their own operating system.

VCS will connect the hardware’s using intelligent software to provide failover, load balancing, and control. when the monitored node or application failed, it will invoke another node or application which is hosted on a node within the cluster.

 

Reference: Symantec

RedHat Enterprise Linux 7 Installation

Will start learning RedHat Enterprise Linux 7 Installation in this post.

We have many new features in RHEL7 and simple differences in installation as well comparing to old version’s that we were given input like hostname, timezone, package selection, network configuration, kdump configuration, etc… in next next screen’s. But, in RHEL7 we can provide those details on a single screen. However all the remaining will be the same.

Using RHEL7 media boot the machine and you will receive a screen like below.

RedHat Enterprise Linux 7 Installation

Now select “Install Red Hat Enterprise Linux 7.3” to begin the installation.

As first part, you will get a screen that is asking you to select the System language and keyboard layout like below.

Then next you will get a screen which is the place to provide all information to install the operating system.

In this screen, you can provide all the information like Software selection, Partitioning in Installation destination tab, time zone, etc…

Now, will edit some of the configuration based on our requirement.

As first, here editing time zone part and selecting Asia/ Kolkata like below.

you can select the time zone in two ways one is by clicking on India over the map and another one is selecting Asia and Kolkata in the drop-down list.

And, click on the done button which is showing the left corner of upper on the screen to complete this part.

Likewise, we should click on done for each and every part.

Now, Click on “Software selection” tab to select packages

Will continue with default one which is “minimal installation”.

Based on the selected packages group, it will install the required packages.

Next, Click on “Installation destination” to create partitions.

We have two option at this stage. One is “Automatically configure partitions” and another one is “I will configure partitioning”

If you select the first option, it will create the partition automatically with LVM and if you select the second option, we need to provide the partition details manually.

Here let us see how to create manual partitions.

Once you selected the second option, you will get a screen asking for partition type Standard, LVM, etc…

select on Standard one to create a normal partition.

and click done to go next screen of partition creation.

It will ask for the mount point with size like below. Below filesystem, creation is compulsory while doing manual partitioning.

  1. boot – Contains bootloader and partition information
  2. / (root)
  3. swap – Virtual memory

Like above will create the three mandate partition to continue the installation.

and click done to go back to the main screen.

and it will ask our confirmation to write the partition changes on the disk. Click “Accept Changes”.

And now, click “Begin Installation” to start the package installation.

In package installation screen, we can see that password has not been set still. So, click on “Root Password” to set the root password. and click done.

See the screen after root password has been assigned.

Once installation completed, will ask for the reboot. Click on “Reboot” button to complete the installation.

We compeleted RHEL7 installation successfully.

 

 

 

 

 

How to boot with an old kernel version in RHEL7

In this post, will see how to boot with an old kernel version in RHEL7. When the updated kernel not suitable for your application or OS not booting.

There might be a requirement to upgrade the operating system or kernel version alone in Linux/Unix machines.

In such case, we might face issue with the upgraded kernel version. To, fix that, follow the below steps.

By default, /etc/default/grub file has entry called GRUB_DEFAULT=saved.

[root@localhost ~]# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rhgb quiet"
GRUB_DISABLE_RECOVERY="true"

This entry instructs the system which kernel will be used to load the operating system by checking the saved_entry in the grubenv file, which is in /boot/grub2/grubenv.

[root@localhost ~]# cat /boot/grub2/grubenv
# GRUB Environment Block
saved_entry=0
#########################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################[root@localhost ~]#

So we can set the default kernel by editing /boot/grub2/grubenv file or using grub2-set-default command.

To do this, select the old kernel to boot the operating system from grub splash screen.

How to boot with old kernel in RHEL7

And use the grub2-set-default command to change the kernel.

Before changing we should remember that, the always updated kernel will be on top and will use numeric value “0” to mention this kernel in command

The old one will be available by next. So, to mention the old kernel will use numeric value “1”. Like this numeric will start from 0.

/boot/grub2/grub.cfg file contains Kernel and initramfs image details.

below command will show us the list of the kernel installed on this machine.

[root@localhost ~]# awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg
Red Hat Enterprise Linux Server (3.10.0-693.17.1.el7.x86_64) 7.3 (Maipo)
Red Hat Enterprise Linux Server (3.10.0-514.el7.x86_64) 7.3 (Maipo)
Red Hat Enterprise Linux Server (0-rescue-ffc8e857b7b84166b88e7b0522c168a4) 7.3 (Maipo)

By default, saved_entry will be the latest one, which you updated.

Using below command will change the default kernel as the old one to boot the operating system without any issue.

[root@localhost ~]# grub2-set-default 1

and now check again in /boot/grub2/grunenv file to verify the default kernel.

[root@localhost ~]# cat /boot/grub2/grubenv | grep saved
saved_entry=1

Now you can see in above screen that the old kernel is set as default one.

Now rebuild the /boot/grub2/grub.cfg file using grub2-mkconfig -o command.

Use the below command in BIOS based machines:

[root@localhost ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-693.17.1.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-693.17.1.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-514.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-514.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-ffc8e857b7b84166b88e7b0522c168a4
Found initrd image: /boot/initramfs-0-rescue-ffc8e857b7b84166b88e7b0522c168a4.img
done

Use below command for UEFI based machines:

[root@localhost ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

finally, restart the machine and check whether the machine booting using old kernel.

reference: Red Hat Document

Limiting CPU and Memory usage to users/groups(CGroups)

In this post we are going to see : Limiting CPU and Memory usage to users/groups.

In large environments, there is a chance to access single system by more than one users at a time. So, user’s can access the resources highly.

For our exercise going to use RHEL7 Operating System.

CGroups will help us to limit the resources by group of users.

We have below users created already to do practise.

[root@server ~]# grep home /etc/passwd
lbcuser1:x:1005:1007::/home/lbcuser1:/bin/bash
lbcuser2:x:1006:1008::/home/lbcuser2:/bin/bash
lbcuser3:x:1007:1009::/home/lbcuser3:/bin/bash
lbcuser:x:1008:1011::/home/lbcuser:/bin/bash

Users are assigned to below mentioned groups.

Groups:    lbcgroup, finance, admin

[root@server ~]# grep "lbcuser" /etc/group
finance:x:1003:lbcuser2
lbcgroup:x:1010:lbcuser1,lbcuser
admin:x:1012:lbcuser3

To work on this, lbcgroup package should be installed and will use /etc/cgconfig.conf and /etc/cgrules.conf to apply the rules overs the users to limit the resources use.

follow the below steps to apply rules by per Group:

[root@server ~]# vi /etc/cgconfig.conf
mount {
 cpu = /cgroup/cpu_and_mem;
 cpuacct = /cgroup/cpu_and_mem;
 memory = /cgroup/cpu_and_mem;
}

group finance {
 cpu {
 cpu.shares="250";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

group lbcgroup {
 cpu {
 cpu.shares="250";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

group admin {
 cpu {
 cpu.shares="500";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

While starting the server, above configuration file will mount cpu, cpuacct and memory subsystems to a cpu_and _memory cgroup.

CPU:

cpu-shares parameter used to assign the the CPU resources which is available to each and every processes. Assigning parameter values as 250, 250 and 500 for finance, lbcgroup and admin groups in cgroup will split the CPU resources in 1:1:2 ratio. If only one process is running, it doesn’t matter in which cgroup it falls. CPU limitation will be applied, when there is more than one process running.

cpuacct:

cpuacct.usage=”0″ this value is used to reset the CPU usage on cpuacct.usage and cpuacct_percpu files. These files contains the total CPU utilized time by all the process.

Memory:

memory.limit_in_bytes=”1G” parameter says that how much memory allowed to use by a cgroup.

memory.memsw.limit_in_bytes=”2G” parameter says that how much swap space allowed to use by a cgroup

cgrulesengd:

Start this daemon using below command:

[root@server ~]# systemctl start cgred

This daemon will help to move process to specific cgroup and for that we need to configure /etc/cgrules.conf like below

[root@server ~]# vi /etc/cgrules.conf
# /etc/cgrules.conf
#The format of this file is described in cgrules.conf(5)
#manual page.

@finance  cpu,memory finance
@lbcgroup cpu,memory lbcgroup
@admin    cpu        admin

Like above will assign rules to group.

In this, process will be moved to cgroup based on which user started this process and belongs to which group.

For example, Process detects the limitations from lbcgroup cgroup, which is started by lbcuser1 user and it will move to /cgroup/cpu_and_mem/lbcgroup/tasks file.

cgconfig:

Start this daemon to create hierarchy of cgroup to set the required parameters  in all cgroups.

[root@server ~]# systemctl start cgconfig

and to make all changes persistent across reboot, configure both(cgred, cgconfig) services to be started by default.

[root@server ~]# systemctl enable cgred

[root@server ~]# systemctl enable cgconfig

 

Reference: Red Hat official documentation

How to install Graphical user Interface/GUI on RedHat 7 Linux

In this post going to see How to install Graphical user Interface/GUI on RedHat Linux.

We have 7 run levels in RedHat and in that, runlevel 5 is used for GUI.

Use below command to change from current runlevel to GUI(before changing to graphical mode, make sure GNOME package installed):

[root@server ~]# init 5

To set GUI as default runlevel, use the below command and reboot the machine.

[root@server ~]# systemctl set-default graphical.target

If without any error runlevel switched to GUI, than package is already installed in your machine.

If you are receiving any error, than you should install the GNOME package.

Let’s see how to install the GUI in RedHat 7.

We will use yum package manager to install the GUI.

We have two types of repository that, one is online and another one is local repository.First decide which repository going to use to install GNOME package.

If you’re machine connected with internet, register in redhat repository using below command.

[root@server ~]# subscription-manager register
[root@server ~]# subscription-manager refresh
[root@server ~]# subscription-manager attach --auto

To use local repository make sure its already configured in your machine. Click here to know how to configure local yum repository.

Use the below command to check the group name for GNOME installation.

[root@server ~]# yum grouplist
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use su bscription-manager to register.
There is no installed groups file.
Maybe run: yum groups mark convert (see man yum)
Available Environment Groups:
 Minimal Install
 Infrastructure Server
 File and Print Server
 Basic Web Server
 Virtualization Host
 Server with GUI
Available Groups:
 Compatibility Libraries
 Console Internet Tools
 Development Tools
 Graphical Administration Tools
 Legacy UNIX Compatibility
 Scientific Support
 Security Tools
 Smart Card Support
 System Administration Tools
 System Management
Done

We should install “Server with GUI” using yum like below.

[root@server ~]# yum -y groupinstall "Server with GUI"

Now successfully installed GUI in our machine. Try to switch using “init 5” command.

Thanks for reading this post.

Reference: Red Hat Discussion

Bash shell script to run more commands which is stored in a file

Bash shell script to run more commands which is stored in a file

You might be tired by finding the right Bash shell script to run more commands which are stored in a file. Here is the script which you are searching…

In this example going to use below commands in the file to execute using the script.

df -h

uname -a

ls -l

netstat

As next step, we are going to create a file with above commands assigned to a variable. If we are using this commands directly without assigning to a variable, the script will not execute the commands properly. Because of space(df -h) which we used in between commands will be taken as a separator by the script. So that only we are saving the commands in a variable.

[root@server ~]# cat > cmd.lst
DF=`df -h`
UNAME=`uname -a`
CAT=`cat /etc/resolv.conf`
NET=`netstat` 
^c
[root@server ~]# 

Then create the script to run the commands which are stored in cmd.lst file

[root@server ~]# cat > cmdscritp.sh
#!/bin/bash
sh cmd.lst
for comm in `cat cmd.lst`
do
 for cmd in `cat cmd.lst | awk -F "=" {'print $1'}`
 do
 echo "Going to execute:" $cmd
 eval $cmd
 if [[ $? -eq "0" ]]
 then
 echo $cmd "executed successfully..."
 else
 echo "last command didn't executed properly. So, Exiting from the script..."
 exit
 fi
 done
done

and now provide the execute permission using chmod command for both files.

[root@server ~]# chmod +x cmd.lst
[root@server ~]# chmod +x cmdscritp.sh

[root@server ~]# ll | grep cmd
-rwxr-xr-x. 1 root root 69 Dec 28 23:58 cmd.lst
-rwxr-xr-x. 1 root root 326 Dec 28 23:58 cmdscritp.sh

Now run the script

[root@server ~]# ./cmdscript.sh 
cmd.txt: line 4: netstat: command not found
cmdscript.sh cmd.txt diff2.sh diff.sh lvcheck.txt post pre sh
Goind to execute: df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 10474496 2097740 8376756 21% /
devtmpfs 1887604 0 1887604 0% /dev
tmpfs 1894500 0 1894500 0% /dev/shm
tmpfs 1894500 8444 1886056 1% /run
tmpfs 1894500 0 1894500 0% /sys/fs/cgroup
tmpfs 378900 0 378900 0% /run/user/0
tmpfs 378900 0 378900 0% /run/user/1000
df executed successfully...
Goind to execute: uname
Linux
uname executed successfully...
Goind to execute: ls
cmdscript.sh cmd.txt diff2.sh diff.sh lvcheck.txt post pre sh
ls executed successfully...
Goind to execute: net
./cmdscript.sh: line 8: net: command not found
last command didnt executed properly. So, Exiting from the script...

 

Script working successfully. Thanks for reading the post and support.

No supported authentication methods available

Error:

Disconnected: No supported authentication methods available (server sent: publickey,gssapi-keyex,gssapi-with-mic)

No supported authentication methods available

Receiving error When trying to access Linux server through putty or other tool using ssh service.

Solution:

  1. Edit /etc/ssh/sshd_config configuration file using vi editor.
        [root@server ~]# vi /etc/ssh/sshd_config
  2. Check and replace with yes for below entry
     PasswordAuthentication no

    changed 

    PasswordAuthentication yes
  3. save and exit from the file using :wq
  4. Than restart the ssh service using below command.
    systemctl restart sshd
  5. Restart the network service using below command.
    systemctl restart network
  6. Now try to access the server and sure it will work. Still if you are facing error in accessing the server, that there might be issue with firewall configuration.

Reference: Super user

Permission handling in Linux

In this post we are going to see(Permission handling in Linux) how to set permission for files and directories in linux/unix.

Before set/unset permission we should check the existing permission for a file usinf ll <filename> command like below.

[root@server ~]# ll abu
-rwxrwxrwx. 1 abu root 113 Dec 11 20:22 abu

We can assign permission based on below categories and same has been display while executing ll or ls –l command.

User:    u

Group:  g

Others:  o

Numeric values used for changing/identifying the permissions:

Read:       4, r

Write:      2, w

Execute:  1, x

Command used for changing file permission:

#Chmod 655 <filename>

Example:

Command to set permission:

We are going to set permission for file abu from 777 to 755 using below command. 755 will have full permission for user, read and execute for group and others.

[root@server ~]# chmod 755 abu
[root@server ~]# ll abu
-rwxr-xr-x. 1 abu root 113 Dec 11 20:22 abu

Also will set the permissions usings characters like below.

Read:        r

Write:       w

Execute:  x

Example:

Command to set permission using characters:

In the below example going to set execute permission alone to others

[root@server ~]# ll abu1
-rwxr-xr--. 1 root abu 0 Dec 11 20:17 abu1
[root@server ~]# chmod o+x abu1
[root@server ~]# ll abu1
-rwxr-xr-x. 1 root abu 0 Dec 11 20:17 abu1

Changing ownership of a file or directory:

#Chwon user:group <filename>

example:

In below example going to change owner of the directory as lbcuser for lbc directory. User has been created already.

Note: Existing owner and group will be root.

before changing owhership:

[root@server ~]# mkdir lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 root root 6 Dec 16 20:33 lbc

after changing ownership:

[root@server ~]# chown lbcuser lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 lbcuser root 6 Dec 16 20:33 lbc

using chown command will change group as well like below.

Going to change group as finance.

[root@server ~]# chown :finance lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 lbcuser finance 6 Dec 16 20:33 lbc

Will change the group alone using chgrp command:

[root@server ~]# mkdir lbc1
[root@server ~]# chgrp finance lbc1
[root@server ~]# ll | grep lbc1
drwxr-xr-x. 2 root finance 6 Dec 16 20:47 lbc1

 

Reference: RedHat Document