Connecting via ssh to the newly created host causes error:
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@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
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IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:AxfpHOVc8NP2OYPGce92HMa5LADDQj2V98ZKgoQHFGU.
Please contact your system administrator.
Add correct host key in /Users/mari/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /Users/mari/.ssh/known_hosts:315
ECDSA host key for 52.1.130.91 has changed and you have requested strict checking.
Host key verification failed.
Reason:
I had another server with the same Public IP, so when I connected to the old saver the host identification has been saved in known_hosts. After a while I have removed old server and created a new one and assigned the PIP. The host identification has changed, but old entries were still saved in known_hosts.
Solution:
Open /Users/mari/.ssh/known_hosts and delete only the line containing mentioned IP (52.1.130.91 in my case), save file and retry the connection. It should work now.
This blog post belongs to my student at Business and Technology University Ivane Metreveli, thank you Ivane for participating in this project.
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 disknow 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:
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.
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):
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!
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 .
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.
DBA Knowledge Base 