Amar Helloween

Today we are going to learn how to fix route issues on Linux. Suppose you have 2 NIC interface (one is for public traffic - 100 GBPS Link and other one in Private interface for private communication 10 GBPS Link ). What is the exact issue ? Initially our customers reported that they were unable to reach internet on the box (They tried performing ping 8.8.8.8 -or- ping google.com). It was not working via both IP and domain name even tried with browser. So lets begin the troubleshooting : Step 1 : Replicate the issue from your side, because we need to be 100% sure before deep diving. Step 2 : We were able to replicate the same. It was 100% packet loss. So now we need to check if the public interface is up and running or not . Our public interface is eth1 so run command : ip a This will show you if interface is UP / Down. Eth1 was up and running here. Step 3 : Next I was interested to see how is the traffic going out - is it crossing any single hop or not , whether Gateway is reachable

Here are the list of some useful Linux commands that's used on a day-to-day work and are equally important for interview purposes.  1. How to check memory usage free -h -h is to make the result readable by humans. 2. How to check disk usage df -h 3. How to check CPU Usage top 4. How to quickly find the process id of a program pgrep <ProcessName> 5. How to find the Linux Kernal version uname -r amar@LPF22E8MA:~$ uname -r 4.4.0-19041-Microsoft 6. How to find the Operating System (OS) version cat /etc/os-release lsb_release -a amar@LPF22E8MA:~$ cat /etc/os-release NAME="Ubuntu" VERSION="20.04 LTS (Focal Fossa)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 20.04 LTS" VERSION_ID="20.04" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_C

Today we will see how one can become a root user if he / she has sudoers access. In some organizations if you try to switch user to root ( sudo su - root ), you may see error like below : Sorry, user <username> is not allowed to execute '/bin/su - root' as root on <hostname> But you can try other method to switch as root user. Lets look into those steps. Method 1 : Type  sudo vi -c '!bash' in the command line console and that's it. Method 2 :   Type   sudo vi a.txt  in the command line console , it will open vi editor just press ESC (Escape) and then :sh and Enter Hope you all enjoyed this little hack, do share your queries in the comment box below.