This post is part 37 of 37 in the series Taming the Terminal

Since we covered SSH in parts 29 & 30, Apple have changed how their desktop OS deals with the passphrases protecting SSH identities (key pairs). This provides us a good opportunity to have a look at the SSH Agent in general, and, how things have changed on the Mac in particular.

The good news is that while things have changed on the Mac, with a small amount of effort, you can get back all the convenience and security you had before.

Read more

Tagged with:

This post is part 36 of 37 in the series Taming the Terminal

The previous 13 instalments in this series related to networking, but we’re going to change tack completely for this instalment, and look at two un-reltaed, but very useful terminal commands – screen, and cron.

screen is a utility that allows for the creation of persistent virtual terminal sessions that you can disconnect from without terminating, and reconnect and pick up where you left off at a later time. screen is particularly useful when used in conjunction with SSH.

cron on the other hand is a system for automatically executing recurring tasks. It’s extremely flexible, and very useful for things like scheduling backups to run in the middle of the night.

Read more

Tagged with:

This post is part 35 of 37 in the series Taming the Terminal

The previous instalment we introduced the HTTP protocol. In this instalment we’ll look at three terminal commands which make use of the HTTP protocol.

We’ll start by browsing from the terminal, and then move on to a pair of very similar commands for making HTTP requests from the terminal. These two commands can do many things, but we’ll focus on two specific use-cases, downloading files, and viewing HTTP headers.

Read more

Tagged with:

This post is part 34 of 37 in the series Taming the Terminal

In the previous instalment we finished a five-part series on SSH. Before moving on, lets take a moment to step back and look at the big-picture. The five SSH instalments are all part of the now long-running series on networking. We have been working our way through the networking stack since instalment 23. We started at the bottom of the stack, and have worked our way up. We are not exploring protocols in the Application Layer.

In this instalment we’re moving on from SSH to HTTP, the protocol that powers the world wide web.

Before we look at some HTTP-related terminal commands, we need a basic understanding of how HTTP works, so that’s what this instalment is all about.

Read more

Tagged with:

This post is part 33 of 37 in the series Taming the Terminal

This is the final SSH instalment. So far we’ve learned how to securely execute terminal commands on remote computers, how to securely copy files across the network using SSH, how to add both security and convenience to both those operations with SSH key pairs, and how to tunnel just about anything through SSH. In this final instalment we’ll look two approaches for creating SSH bookmarks, SSH config files, and SSH GUIs.

Read more

Tagged with:

This post is part 32 of 37 in the series Taming the Terminal

This is the fourth SSH instalment. So far we’ve learned how to securely execute terminal commands on remote computers, how to securely copy files across the network using SSH, and how to add both security and convenience to both those operations with SSH key pairs.

As we saw in the previous instalment, SSH’s ability to provide a secure connection between two computers can be used in many different ways. In this instalment we’ll learn about three more ways to encapsulate other network traffic within an SSH connection, adding encryption to that traffic.

Running commands and copying files are the kinds of things most people do, so the three SSH instalments to date have been quite generally applicable. That is not the case for this instalment. The three SSH features we’ll be discussing are all very useful to those who need them, but only a minority will have a use for any one of these features. However, even if you don’t need these features today, I would argue that it’s good to know these features exist, because they could well solve a problem you’ll have in the future.

There will be illustrations of the uses for these technologies, but not commands you type into your terminal to play along at home. That makes this an unusual instalment, but I hope you will still find it worthwhile.

Read more

Tagged with:

This post is part 31 of 37 in the series Taming the Terminal

In Part 29 of n we learned how to use SSH to execute commands on a remote computer. In the previous instalment we learned how to add security and convenience to SSH connections using SSH key-pairs.

The most important thing SSH provides is an encrypted connection between two computers. As we’ve seen, that encrypted connection can be used to securely issue terminal commands to a remote computer, but that same secured channel can also be used to secure other network connections between computers. In this instalment we’ll look at three different ways of securely copying files between computers through an SSH connection, and in the next instalment we’ll look at tunnelling just about any network connection through an SSH connection.

Read more

Tagged with:

This post is part 30 of 37 in the series Taming the Terminal

In the previous instalment we saw how we can use SSH to execute a single command on a remote computer, or, to get a command shell on a remote computer. We also saw how SSH uses host keys to protect us from man-in-the-middle (MITM) attacks.

In this instalment we’re going to look at how we can improve both SSH security and convenience with SSH keys.

Read more

Tagged with:

This post is part 29 of 37 in the series Taming the Terminal

In the previous six instalments we looked in detail at how TCP/IP networks tick. In these instalments we worked our way up from the bottom of the four-layer TCP/IP network model to the top, finishing off with a look at two protocols in the Application Layer at the top of the stack. Those two protocols, DHCP & DNS exist in the top layer, but are different to most other top layer protools in that they can reasonably be described as forming part of the infrastructure of the internet. The email and web protocols may site within the same network layer, but they still rely on DNS to function.

For the remainder of the networking section in this series we’ve moving away from infrastructure-like protocols, and focusing on the user-facing Application Layer protocols. The first of these we’ll be looking at is the Secure Shell, or SSH. This protocol is one of the absolute work-horses of the internet, and a vital tool for all Linux, Unix, and OS X sysadmins.

At it’s simplest level SSH allows you to execute commands on a remote computer, but because it was designed around the concept of a secure tunnel between two systems, SSH has expanded to allow all kinds of advanced features. The least-generous description of this could be that SSH has become a kind of sysadmins fridgeoven. But I don’t buy that, I prefer the alternative interpretation – it simply makes sense not to re-invent the wheel, and to allow as much information as possible to flow throw the secure connection SSH provides between the two end-points.

Today we’re just going to start with the basics, but in future instalments we’ll move on to the more advanced features.

Read more

Tagged with:

This post is part 28 of 37 in the series Taming the Terminal

In part 23 of n we took a big-picture look at how TCP/IP networking works. As a quick reminder, the most important points were:

  • Our computer networks use a stack of protocols known as TCP/IP
  • We think of the stack of protocols as being broken into four layers:
  • The Link Layer – lets computers that are on the same network send single packets of data to each other
  • The Internet Layer – Lets computers on different networks send single packets of data to each other
  • The Transport Layer – lets computers send meaningful streams of data between each other
  • The Application Layer – where all the networked apps we use live
  • Logically, data travels across the layers – HTTP to HTTP, TCP to TCP, IP to IP, ethernet to ethernet, but physically, data travels up and down the stack, one layer to another, only moving from one device to another when it gets to the Link Layer at the very bottom of the stack.
  • Since that big-picture introduction we’ve looked at the first three layers in detail, and we’ve also looked at two layer-4 protocols that function as part of the network infrastructure – DHCP for the automatic discovery of network settings, and DNS for mapping domain names to IP addresses. Later in the series we will move on to look at some more layer 4 protocols, but before we do I want to consolidate what we’ve learned so-far into a strategy for debugging network problems. In short – how to get from a vague complaint like “the internet is broken” to a specific problem that can be addressed.

    Read more

    Tagged with:

    keep looking »