Add new virtual machine in VBox and install Oracle Linux

Intro:

This blog post belongs to my student at Business and Technology University Ivane Metreveli, thank you Ivane for participating in this project.

  1. First of all, you need to download Oracle Linux iso file from edelivery.oracle.com or from oracle.com. After that, run VirtualBox, click New button and create new virtual machine:

2. Set Name of the Virtual Machine and select operation system as follows, click Next

3. Select appropriate RAM amount, 3GB RAM is recommended for normal processing, click on Next button and jump to next step

4. Now, Select Create a virtual hard disk now option and click Create button

5. Select VDI(virtualbox Disk image)

6. Select Dynamically allocated if you don’t want take hard disk space immediately

7. Select file size (disk size for VB) and the location, click Create button to finish virtual machine creation process

8. Virtual machine is already is created. Before we open/start VM, we load iso file in the machne, click Settings and follow me

9. Navigate to Storage and click CD icon,  on the right side of the window, under attributes, click CD icon and add virtual machine’s .iso file.

10. After that, you can click start button

11. Select .iso files or click folder icon and open folder where .iso file is located, select it and click start

12. Next step is OS installation process, here you select Install Oracle linux 7.6 and click enter to start installation process:

13. Select system language and click continue

14. Select installation destiantion

15. Select the disk where you want to install system. You can select virtual disk, that you have created in the previous step or add a new one. Select disk and click Done button;

16. Now all parameter is ready. Click Begin Installation and wait for finishing the process

17. Set password and click Done

18. Installation is in progress, need to wait more

19. Installation proess is finished, click Roboot button and move to the next step:

20. Installation is finised now, you can start working with Oracle Linux:

Install Linux in Virtual Box

Intro:

This blog post belongs to my student at Business and Technology University Saba Lapanashvili, thank you Saba for participating in this project.

Requirements:

– VirtualBox
– Linux iso file ( For example Linux Mint 15 )

Step 1: Choose System Type

– After installing VirtualBox, click New
– Fill the Name field: e.g Linux Mint 15
– Select Type: Linux
– Select Version: Ubuntu

Step 2: Select the Amount of RAM

– Select the amount of RAM, e.g 2048 MB = 2 GB

Step 3: Configure Hard Disk Settings

– Choose Create a virtual hard drive now, to make a virtual disk space
– Select the VDI 
– Choose Dynamically allocated
– Select the amount of hard drive size

Step 4: Choose Linux ISO File

Now we have done hardware settings

– Click Start to launch system
– Choose your system iso file from your computer, for example my system iso file is (linuxmint-15-cinnamon-dvd-64bit.iso)

Step 5: Install Linux and Make Account

– Click on the Install Linux Mint
– And select Erase disk and install Linux Mint
– Then press Install Now
– Make your account
– Press Continue

Step 6: Congratulations

Congratulations now you have Linux on your Windows.

Find 5 biggest files in Linux

I have used this command many times, but the interval between each usage is so big that I almost always forget the syntax.

So here it is:

# du -a / | sort -n -r | head -n 5

51190272	/
37705424	/root
33040524	/root/apache-tomcat-7.0.53
32802516	/root/apache-tomcat-7.0.53/logs
32802440	/root/apache-tomcat-7.0.53/logs/catalina.out

Reduce high CPU usage by TFA

Problem:

Cluster nodes experienced high CPU usage, after investigation one of the top CPU consumers on the server has been found to be a TFA process (2nd place):

 # Fri Feb 19 17:44:01 2021
AllCPU  OneCPU  PID     User    PR      NI      STime   RSS     Name
--------------------------------------------------------------------------------
11.75%  94.02%  23895   root    20      0       17:43   87M     ora_m001_ORCL2
1.42%   11.39%  2468    root    20      0       Feb02   736M    /opt/oracle.ahf/jre/bin/java -server -Xms256m -Xmx512m -Djava.awt.headless=true -Ddisable.checkForUpdate=true -XX:HeapDumpPath=/u01/app/oracle.ahf/data/rac02/diag/tfa -XX:ParallelGCThreads=5 oracle.rat.tfa.TFAMain /opt/oracle.ahf/tfa

Workaround:

In newer version of TFA, you can set CPU resource limit.

tfactl setresourcelimit 
 [-tool tool_name] 
 [-resource resource_type] 
 [-value value]

To limit TFA to a maximum of 50% of a single CPU, run the following:

# tfactl setresourcelimit -value 0.5

For more information, please check TFA official documentation.

If you don’t have newer version of TFA, you need to upgrade it first.

How to identify OS is Oracle Linux or RHEL?

There are several ways to identify that, I will suggest one of them using rpm -qf, that finds out what package a file belongs to:

Oracle Linux:

#  rpm -qf /etc/redhat-release
oraclelinux-release-7.8-1.0.7.el7.x86_64

RHEL:

# rpm -qf /etc/redhat-release
redhat-release-server-7.8-2.el7.x86_64

Boot in single user mode and rescue your RHEL7

Problem:

One of our customer incorrectly changed fstab file and rebooted the OS. As a result, VM was not able to start. Fortunately, cloud where this VM was located supported serial console.

Solution:

We booted in single user mode through serial console and reverted the changes back. To boot in single user mode and update necessary file, do as follows:

Connect to the serial console and while OS is booting in a grub menu press e to edit the selected kernel:

Find line that starts with linux16 ( if you don’t see it press arrow down ), go to the end of this line and type rd.break.

Press ctrl+x.

Wait for a while and system will enter into single user mode:

During this time /sysroot is mounted in read only mode, you need to remount it in read write:

switch_root:/# mount -o remount,rw /sysroot
switch_root:/# chroot /sysroot

You can revert any changes back by updating any file, in our case we updated fstab:

sh-4.2# vim /etc/fstab

You are a real hero, because you rescued your system!

pam_systemd(sshd:session): Failed to create session: Failed to activate service ‘org.freedesktop.login1’: timed out

Problem:

1. Slow ssh connections
2. System seems slow when trying to su to another user

/var/log/secure contains the following errors:

pam_systemd(sshd:session): Failed to create session: Failed to activate
service 'org.freedesktop.login1': timed out

Solution:

1. Restart systemd-logind service

# systemctl restart systemd-logind

2. Restart server

# reboot 

Note that the mentioned solutions are considered as temporary solutions (Frankly, I’ve never seen this error after restart. The problem happened with our two customers, who changed sshd_config file and did “something” after that, so the problem was caused by humman error in my all cases), for more information about this problem please see article at redhat site
https://access.redhat.com/discussions/3536621 .

Azure: yum install returns [Errno 14] curl#58 – “SSL peer rejected your certificate as expired.”

Action:

I have deleted tigervnc rpm and was trying to reinstall it but got the following error:

yum install tigervnc*

https://rhui-3.microsoft.com...x86_64/dotnet/1/debug/repodata/repomd.xml: [Errno 14] curl#58 - "SSL peer rejected your certificate as expired."
Trying other mirror.

Actually, the problem is not related to tigervnc only, it is global. During this time I was not able to run yum update or any installation using yum.

Causes:

Red Hat Update Infrastructure (RHUI) certificate has expired and it needs to be updated.

Solution:

Update RHUI certificate using the following rpm:

For RHEL 7:

# curl -o azureclient.rpm https://rhui-1.microsoft.com/pulp/repos/microsoft-azure-rhel7/rhui-azure-rhel7-2.2-74.noarch.rpm
# sudo rpm -U azureclient.rpm

For RHEL 6:

# curl -o azureclient.rpm https://rhui-1.microsoft.com/pulp/repos/microsoft-azure-rhel6/rhui-azure-rhel6-2.2-74.noarch.rpm
# sudo rpm -U azureclient.rpm

Linux: Rename files from uppercase to lowercase

If you have downloaded Oracle 18c installation files, you may need to change downloaded file  names from uppercase letters into lowercase. 🙂

[root@rac1 ~]# cd /sw
[root@rac1 sw]# for i in LINUX.X64_180000_*; do mv $i `echo $i |tr [:upper:] [:lower:]`; done

You may think these are just two files and why I need script? I can do it manually.. 🙂
You are right , but scripting is much more fun. Good luck!

Change timezone on Linux using /etc/localtime file

Assume we have timezone UTC:

[root@oradbfw-hq01-mgmt ~]# date
Mon Sep 11 09:29:27 UTC 2017

On many distributions , like OEL, CentOS.. . the timezone is conntrolled by localtime file located in /etc directory.

# cd /etc

Localtime is a symbolic link , so we can remove it

# rm localtime

All timezones are located under /usr/share/zoneinfo.
I live and my servers are located in Tbilisi, Georgia. So searching my timezone file:

[root@oradbfw-hq01-mgmt etc]# ll /usr/share/zoneinfo/Asia/Tbilisi
-rw-r–r–. 1 root root 1024 Mar 24 09:21 /usr/share/zoneinfo/Asia/Tbilisi

My country is not in Asia, but in Europe 🙂 this condition changed recently so Linux has not updated and still thinks we in Asia. (Don’t tell this to my goverment 🙂 )

Let’s create correct symbolic link:

# cd /etc
# ln -s /usr/share/zoneinfo/Asia/Tbilisi localtime

Let’s check that it was changed:

[root@oradbfw-hq01-mgmt etc]# date
Mon Sep 11 13:47:04 +04 2017