RedHat – Useful YUM and RPM commands

Install the package YUM installs the package if it is not already present and updates it with the latest version available from repo if the package already installed and present. #yum install <package> Check which package (available from repo) provides the binary file/command. #yum provides <binary file/command> Often we want to see what are the … Continue reading RedHat – Useful YUM and RPM commands

AWS EC2 Linux Boot Problems – Root Volume

Below are the step by step instructions to recover EC2 instance if the system is not able to boot properly. So far I have seen couple of scenarios where it helped: -          Corrupted latest kernel ( initrd image is missing ) -          Not able to mount File system because of wrong entry in /etc/fstab and … Continue reading AWS EC2 Linux Boot Problems – Root Volume

Docker – Sharing data between containers

Procedure 1: Using Data Containers Step 1 - Create Container Data Containers are containers which sole responsibility to be a place to store/manage data. Like other containers they are managed by the host system. However, they don't run when you perform a docker ps command. To create a Data Container we first create a container with a … Continue reading Docker – Sharing data between containers

Docker – difference between CMD and ENTRYPOINT

The CMD line in a Dockerfile defines the default command to run when a container is launched. If the command requires arguments then you need to use an array, for example ["cmd", "-a", "arga value", "-b", "argb-value"], which will be combined together and the command cmd -a arga value -b argb-valuewould be run. An alternative approach to CMD is ENTRYPOINT. While … Continue reading Docker – difference between CMD and ENTRYPOINT

RedHat – Rebuild corrupted rpmdb

The "rpmdb" is broken and not able to run any of the rpm commands. #rpm -qa rpmdb: Thread/process 3392/140287890028448 failed: Thread died in Berkeley DB library error: db3 error(-30974) from dbenv->failchk: DB_RUNRECOVERY: Fatal error, run database recovery error: cannot open Packages index using db3 -  (-30974) error: cannot open Packages database in /var/lib/rpm rpmdb: Thread/process … Continue reading RedHat – Rebuild corrupted rpmdb

Linux – Users and Groups – Part 1

Ok.. Lets start with creating a group called "dba" and create user "oracle" belongs to "dba" group. We could see that from "/etc/passwd" that oracle user id is 1521 and primary group id is 5000. But we haven't set the password yet for "oracle" user. If we watch closely "/etc/shadow" password the second column is !! which … Continue reading Linux – Users and Groups – Part 1

AWS Autoscaling – Min Desired Max

As mentioned here : MIN: This will be the minimum number of instances that can run in your auto scale group. If your scale down CloudWatch alarm is triggered, your auto scale group will never terminate instances below this number. DESIRED: If you trip a CloudWatch alarm for a scale up event, then it … Continue reading AWS Autoscaling – Min Desired Max