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Linux How-To Articles and Guide

Tutorials, tips, and guides for users of Linux operating systems.

How to use parallel ssh (PSSH) for executing ssh in parallel on a number of Linux/Unix/BSD servers

Recently I come across a nice little nifty tool called pssh to run a single command on multiple Linux / UNIX / BSD servers. You can easily increase your productivy with this SSH tool.

More about pssh

pssh is a command line tool for executing ssh in parallel on some hosts. It provides specialties includes:

  1. Sending input to all of the processes
  2. Inputting a password to ssh
  3. Saving output to files
  4. IT/sysadmin taks automation such as patching servers
  5. Timing out and more

Let us see how to install and use pssh on Linux and Unix-like system.


How to protects Linux and Unix machines from accidental shutdowns/reboots with molly-guard

Oops! I did it again. I thought I was logged into my home server. Turns out I rebooted the db server. Another my not so favorite is typing "shutdown -h 0" into the wrong terminal. I know a few people who have admitted to doing that here.

My anger that can't be contained
Is there any end to the madness? Do I need to suffer from accidentally random reboots and shutdowns? After all, it is human nature to make mistakes, but one should not keep on making the same mistakes again and again.

Tip: How to start OpenVPN server when systemd based service start to refuse on boot

For some weird reason, I can not get my OpenVPN server to come up at boot time using systemd on an Ubuntu Linux 16.04 LTS server. I have tried a few settings but failed so far.

How to speed up OpenSSL/GnuPG Entropy For Random Number Generation On Linux

Entropy is nothing but the measure of "randomness" in a sequence of bits. The PRNG ( pseudorandom number generator ) is a special device (e.g. /dev/random on Linux) to create randomness from server hardware activities. It uses interrupts generated from the keyboard, hard disk, mouse, network and other sources. The random number generator gathers environmental noise from device drivers and other sources into an entropy pool. The randomness usually used for security purposes like creating TLS/SSL keys and the quality source of random bits is critical. For example, OpenSSL APIs can use quality randomness to make your program cryptographically secure. However, a poor source of randomness could result in loss of security. In this post, I will cover haveged and rng-utils/rng-tools to generate random numbers and feed linux random device for your virtual or dedicated Linux server.

Disabling Google Chrome PDF viewer

Google Chrome has "Chrome PDF Viewer" to view or open pdf files. It is an unwanted feature. I do not need it at all. I want my PDF open in Preview on a MacOS X or default pdf viewer in Linux. This feature was hidden. I want to disable it from my Google Chrome browser because it was slow scrolling with a large pdf file sizes.

Accessing Internet from cloud VM when you have only private network enabled

We have a couple of virtual servers hosted with Softlayer for processing data and backup purpose. The public interface is completely turned off i.e. no Internet access. We can only access VMs using a VPN. It resulted in decreased costs and many security problems for backend servers. However, when you order "Private Network Only" cloud VM, you cannot route outgoing traffic to the Internet using your VM.

Debian Linux 8.3 “jessie” released and here is how to upgrade it from 8.2 to 8.3

Debian 8.3 DesktopThe Debian GNU/Linux project has released an updated version of its stable distribution Debian 8 ("jessie"). You must update to get corrections for security problem as this version made a few adjustments for the serious issue found in Debian 8.2.

Rollback an apt-get upgrade if something goes wrong on Debian / Ubuntu Linux

Rolling back to the previous version may solve the problem or free the disk space. Both CentOS/RHEL support rollback feature, but I learned hard way both Debian and Ubuntu does not support rollback feature yet.

I use the gpass password manager to store my randomly generated unique password for each site. However, many sites such as net banking prevent you from pasting a password when signing up. The site owner or webmaster disables pasting into password input fields. Want to paste your password on such site? Give it a try to don't f*ck with paste Google Chrome extension.

15 Useful Linux and Unix Tape Managements Commands For Sysadmins

Tape devices should be used on a regular basis only for archiving files or for transferring data from one server to another. Usually, tape devices are all hooked up to Unix boxes, and controlled with mt or mtx. In this tutorial you will learn about:

  • Tape device names
  • Basic commands to manage tape drive
  • Basic backup and restore commands