Registering your RHEL instance with Red Hat is straightforward assuming that you already have an account:

# subscription-manager register --username <your-rh-user> --password <password>

List the available repos or just go with a default:

# subscription-manager list --available # subscription-manager attach --auto

Then you can do your update:

# yum update

Did you know that although you can install RHEL from an ISO, you can also download a QCOW2 image from Red Hat. However, when you try to start it up under virt-manager you’ll see that it boots to a root prompt and you don’t know what the password is. This can be fixed by running the following from the host’s terminal:

# virt-customize -a <qcow2-image-file-name> --root-password password:<password>

There are a lot of tools out there that can help you to do this that are both GUI or command line-based but sometimes you’re on a production server that may have limited tools and sometimes the simplest tools are best in cases like this.

List the processes that are not owned by you that are using a lot of CPU:

$ ps aux --sort=-%cpu | grep -m 8 -vwhoami

Listing installed packages with YUM:

$ sudo yum list installed

To display details about a package:

$ yum info nginx

You can cat all installed packages to a file, copy the file to another machine and duplicate the system:

$ sudo yum list installed > installed-packages.txt $ sudo yum -y install $(cat installed-packages.txt)

List installed packages with RPM:

Let’s say that you want to delete the last 3 commits that you’ve already pushed to the remote repository. In this example, you want 566dab6 to be the new HEAD revision.

$ git log --pretty=oneline --abbrev-commit 57bc36b (HEAD -> master, origin/master, origin/HEAD) 3nd set of bad entries on 6th commit dfb4bd3 2nd set of bad entries on 5th commit 0fd1e16 First set of bad entries on 4th commit 566dab6 Yet more good entries on third commit d50370a More good entries on second commit b5fbc6d Good entries on first commit 2cad4c7 Initial commit

If you’re using a laptop with an external monitor and you’ve recently installed Solus OS you might have noticed that the laptop goes to sleep when you close the lid and there is no way to adjust for this in the power settings. You can get around this by manually editing /etc/systemd/logind.conf, then uncommenting and changing the line:

#HandleLidSwitch=suspend

to

HandleLidSwitch=ignore

Note: The ‘#’ (comment) at the beginning of the line needs to be removed and the value needs to be changed from suspend to ignore.

If you are experiencing tearing while using Firefox you may want to see if graphics accelleration is enabled on the browser. You can try this tip to force hardware accelleration on in the browser.

First, check to make sure that your Linux desktop installation supports it by running the following command and making sure that direct rendering returns Yes:

$ glxinfo | grep render direct rendering: Yes

If you have a file (or a stream) that has blank lines you want to remove, you can use this command:

$ grep -v "^ *$" file-with-blanks.txt > output-file.txt

where file-with-blanks.txt is the input file and has blank lines and output-file.txt will be the output file without the blank lines.

You have to keep the space between the ^ and the *$ otherwise blank lines which include spaces will not be removed.

You can use ffmpeg to convert webm to mp4 on the command line very easily:

$ ffmpeg -i file.webm -c copy file.mp4

This will stream copy (re-mux) and avoid re-encoding.

What is KDbg?

From the homepage:

KDbg is a graphical user interface to gdb, the GNU debugger. It provides an intuitive interface for setting breakpoints, inspecting variables, and stepping through code.

KDbg requires KDE, the K Desktop Environment, but you can of course debug any program.

Here’s how to install it on Slackware 15 but this should work on any system that has KDE:

$ git clone -b maint https://github.com/j6t/kdbg.git $ cd kdbg/ $ cmake . $ make $ su -c "make install"