GNU/Linux

If you make a change to a configuration file that needs to be reflected in your Linux boot process (such as mdadm.conf), you'll need to add it to your initramfs image.
This process varies by distribution (although most that I have used share the method I describe for Debian).

To update initramfs for Debian, run the command:
update-initramfs -u

In Fedora, run the command
dracut -f /boot/initramfs-currentimage
where initramfs-currentimage is replaced with the name of the image you are currently using.

You read that right. Today I had a partition with over 150 gigabytes of space left on it and a drive error reporting that said partition was full. Not only that, but this was an important partition for me, the one that I keep in a mirrored RAID because it stores the main copy of all my school work, programming and more, so I was very concerned about disk errors.

Sometimes when you are working in your Bash terminal, something goes wrong.
It might have been a program that output strange symbols, or maybe you ran the cat command on a binary file. But, no matter how it happened, it can make your terminal essentially useless until you restart it.
Fortunately, these problems were anticipated by the creators of Bash, and a command exists to set the terminal right.
Simply run reset and all should be well once more, returning you to the joy of the command line interface.

Some Linux distributions allow you to install all of your partitions, save the boot partition, onto encrypted partitions. Doing this can be a big increase to the security of your data, should your computer be stolen, but can be an inconvenience when installed on a server that has no input devices connected. Fortunately, initramfs, the same program allowing you to boot an encrypted root partition in the first place, can also be configure to allow ssh connections.

All of the following must be done as root.

Initramfs (wikipedia) is a temporary filesystem that can boot a Linux system. Using initramfs allows you to use complex file partition schemes for your root directory, such as storing your root on a raid array, or on an encrypted partition.
Because it is designed to do such complex tasks, it allows for a number of utilities to be installed, including a basic shell (Busybox), and an ssh server (dropbox).

A SSH Key allows you to log into a remote server without ever having to enter the password for you user on that server. In some situations, you can use this to increase security, by configuring the remote host to only allow SSH to be used when the client has a key. It can also be useful when the remote host does not have a password, such as when using Dropbear on initramfs. Or, if you need to be able to set up a cron job that can log onto a remote host, you could setup a passwordless key (although there are inherent risks to doing so) and use that to allow the log on.

If you are setting up a static IP address for a computer and need the gateway, finding the gateway address is simple, if you have a computer already setup on the network.
Below is a command which you can run on the configured computer to find the IP address of your gateway.

route -n

You should see at least one entry. If you see several, pick the entry under Gateway that is not 0.0.0.0
This number should be the IP address for your gateway.

In a home network, this is likely the same address as your router.

This article covers how to move your OpenPGP key between computers, and is part of a series in communications security.
The specifics cover moving between Linux computers using GnuPG, although many of the steps will apply to Windows running GnuPG (the main difference should be locating the location of the GnuPG folder under Windows).

This post follows Uploading Your Public Key to a Key Server.
See Security for more posts in the series on communications security.