Category Archives: Linux

Build large environments in no time on Ubuntu using conjure-up

Whether you need to build a Kubernets cluster, an openstack instance, a hadoop cluster…etc, Canonical has developed a tool called conjure-up. This tool can build these whole environments for the purpose of development and testing, or small environments in a … Continue reading

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What to do if docker on Ubuntu doesn’t recognize addition of a user to its group when using PBIS with AD

You add a user to group docker so that you can run docker commands without having to be root or a sudoer. On an Ubuntu 16.04 server which authenticates against AD using PBIS, I added users to group docker, but … Continue reading

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Install docker on multiple Ubuntu Xenial hosts with Ansible

Ansible is an amazing piece of configuration management software. Among its amazing features is that it’s totally agentless and the only 2 packages that it needs on any host are python and an SSH server. Today we will create a … Continue reading

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How to clear your bash history

For old commands, just edit .bash_history and delete whatever you want from inside. For commands in the current session, just run this command before you exit: unset HISTFILE The $HISTFILE environment variable is the one which holds your commands and … Continue reading

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Fix Slow SFTP/SCP File Upload Rate and Stalling caused by TCP SACK

In brief, sometimes a conflict occurs between some firewalls and the TCP SACK. In my case, the upload was severely affected and reached upload speeds of a few kilobytes over a LAN! The following command disables TCP SACK and fixes … Continue reading

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Reclaim storage space from qcow2 image after moving

After it is moved to another host, since it is a sparse file, the qcow2 takes the full space, e.g. if it was dynamically set to 100GB, it will take 100GB, even if only 50 GB were actually used. I … Continue reading

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Securely delete files/folders in Ubuntu

In brief, you should NEVER trust your HDD before handing it over to someone else! The solution to this would be either wipe the whole HDD or at least wipe the files/folders that you need to keep out of reach. … Continue reading

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