Manipulating text with sed

The sed utility can be used to print the contents of a file, substitute a line (or multiple lines), and then save the file. In contrast to grep, sed can substitute a line or multiple lines in a file and perform an in-place update of that file.

The simplest sed invocation when substituting foo for bar is:

$ sed 's/foo/bar/' inputfile
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How To Simulate Linux Commands

Every Linux command has one or more options and flags to perform different operations. One of the useful and important option allow us to simulate Linux commands but do not actually change the system. For instance, we can simulate the process of installation or removal of a package or program, but without actually installing or removing the intended package from a Linux system.

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The /etc/shadow File

There are several different authentication schemes that can be used on Linux systems. The most commonly used and standard scheme is to perform authentication against the /etc/passwd and /etc/shadow files.

/etc/shadow is a text file that contains information about the system’s users’ passwords. It is owned by user root and group shadow, and has 640 permissions.

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Replacing rc.local in systemd Linux systems

Missing rc.local for adding commands to run on startup? Here’s how to set up similar functionality with today’s systemd.

The rc.local file was—and in some cases still is—the place for Linux sysadmins to put commands that need to be run at startup. Use of the rc.local file is not only deprecated but after a couple of hours worth of attempts, was not working in any event. This despite the fact that the systemd documentation mentions the use of a “generator” that generates systemd services from an rc.local file if one exists.

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Using lsof to Recover Deleted Files

If an open file is deleted accidentally, it is possible to use lsof to recreate a copy of the file; provided this is done before the file is closed by the application holding it open.

If you have inadvertently removed a file from the filesystem it is still recoverable if the application using the file it still running. This is because the inode is still open and therefore the data blocks are still on the disk until the application closes the file or exits.

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Create test Apache site with Docker

After creating your EC2 instance and connecting using PuTTY, this tutorials shows steps on how to run docker and setup a test Apache site using a docker image. This tutorial aims to introduce the basic operation of docker and how to use it on a Linux environment.

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Connect to Linux EC2 instance using PuTTY

When you create a new EC2 instance and created new keys, the keys are on the pem key format. This is used for SSH connection and is usable from a Linux terminal or OSX. However, if you are from windows and you use PuTTY to connect to your EC2 instance, you need to convert your pem key to ppk format which is accepted by PuTTY.

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