linux

619 Articles

Under The (Linux) Hood

November 19, 2016 by 53 Comments

We’ve often heard that you don’t need to know how an engine works to drive a car, but you can bet that professional race car drivers know. By analogy, you can build lots of systems with off-the-shelf boards like Raspberry Pis and program that using Python or some other high-level abstraction. The most competent hackers, though, know what’s going on inside that Pi and what Python is doing under the hood down to some low level.

If you’ve been using Linux “under the hood” often means understanding what happens inside the kernel–the heart of the Linux OS that manages and controls everything. It can be a bit daunting; the kernel is simple in concept, but has grown over the years and is now a big chunk of software to approach.

Your first embedded system project probably shouldn’t be a real time 3D gamma ray scanner. A blinking LED is a better start. If you are approaching the kernel, you need a similar entry level project. [Stephen Brennan] has just the project for you: add your own system call to a custom Linux kernel.

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Turn That Old Tablet Into A Sub-$100 Linux Laptop

November 5, 2016 by 43 Comments

Tiny laptops have always been devices that promise so much, yet fail somehow to deliver. From the Atari Portfolio palmtops through to the recent crop of netbooks they have been either eye-wateringly expensive if they are any good, or so compromised by their size constraints as to be next-to-useless. We’ve seen DOS, EPOC, Windows, WinCE, Palm OS, Linux distros and more in tiny form factors over the years, yet few have made a significant mark.

The prospect of a “proper” computer in your hand isn’t something to abandon just yet though. We are now reaching the point at which the previous generation of higher-end Android tablets are both acceptably powerful and sufficiently numerous as to be available at a very reasonable price. Perhaps these can provide the tiny laptop seeker with a basis for something useful. [NODE] certainly thinks so, because he’s produced a nice little Ubuntu laptop using a second-hand Nexus 7 tablet and a Bluetooth keyboard case. Android is replaced with an Ubuntu image, and a cardboard cut-out display bezel is held in place with magnetic strips. A step-by-step guide has been put up to help others interested in following the same path.

This is not the most amazing of hardware hacks, in that it involves mostly off-the-shelf items and a piece of software. However it’s worth a look because it does provide a route to a very acceptable little Linux laptop for an extremely reasonable price. One concern is that the Ubuntu version seems not to be a recent one, however we’re sure readers will point at any newer distribution builds in the comments. If you fancy a look at the finished laptop he’s posted a video which we’ve included below the break.

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SSH Enters The Mosh Pit

November 1, 2016 by 8 Comments

With so many systems depending on Linux, the secure shell SSH has become a staple for many developers. If you are connected to your Raspberry Pi via a cable or a wireless router a few feet away, SSH can provide you with an encrypted connection straight to the box. However, if you have a system out in a swamp somewhere with intermittent slow network access, SSH can be a real pain. When your IP address can change (for example, roaming on a cellular network), SSH has problems, too.

To combat these and other problems, you might consider an open source program called Mosh (mobile shell). There’s two parts to Mosh. One part works as a server while the other is the client application. Neither of these require root access. You can see a video about Mosh below.

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When Your Screen Breaks In The Himalayas

October 24, 2016 by 26 Comments

If you’ve ever had the screen break on your laptop, you’ll know it can be rather annoying to have to use an external monitor for a while as you either wait for a replacement panel to arrive from the other side of the world, or wait for that new laptop you were just desperate for an excuse to upgrade to.

Spare a thought, then, for [tom bh] whose laptop screen broke while he was in Ladakh, Northern India. Two days bus ride from the nearest city in which he could hope to source a replacement part, he had to make do with the resources in front of him. A laptop with a broken screen, and his Android phone.

He was fortunate in that a few lines at the top of the screen still worked intermittently. So after logging in blind and finding himself in a shell, he could execute commands and then scroll the results up to the point at which they were visible. He first enabled an SSH server, then connected his phone via USB. A bit of work to find the laptop’s IP address, and he could get himself a laptop shell on his phone with an Android SSH client. He goes into detail about how he was able to use the laptop’s keyboard to emulate a Bluetooth device which he connected to the phone. He could then run a VNC server on the laptop and connect to it with a VNC client on the phone, resulting in a phone-sized laptop display using the laptop’s keyboard as input. Not a perfect physical terminal by any means, but enough for him to continue working.

His writeup is an especially interesting read for its side-by-side evaluation of the various different application choices he made, and contains some useful suggestions as to how anyone might prepare themselves for a dead screen related emergency.

We’ve featured a dead-screen laptop connected as a serial terminal with an Arduino in the past, but unlike this one that only gave its owner a prompt.

Via Hacker News.

A Slice Of Ubuntu

October 20, 2016 by 24 Comments

The de facto standard for Raspberry Pi operating systems is Raspbian–a Debian based distribution specifically for the diminutive computer. Of course, you have multiple choices and there might not be one best choice for every situation. It did catch our eye, however, that the RaspEX project released a workable Ubunutu 16.10 release for the Raspberry Pi 2 and 3.

RaspEX is a full Linux Desktop system with LXDE (a lightweight desktop environment) and many other useful programs. Firefox, Samba, and VNC4Server are present. You can use the Ubuntu repositories to install anything else you want. The system uses kernel 4.4.21. You can see a review of a much older version of RaspEX  in the video below.

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Make Any PC A Thousand Dollar Gaming Rig With Cloud Gaming

October 19, 2016 by 71 Comments

The best gaming platform is a cloud server with a $4,000 dollar graphics card you can rent when you need it.

[Larry] has  done this sort of thing before with Amazon’s EC2, but recently Microsoft has been offering a beta access to some of NVIDIA’s Tesla M60 graphics cards. As long as you have a fairly beefy connection that can support 30 Mbps of streaming data, you can play just about any imaginable game at 60fps on the ultimate settings.

It takes a bit of configuration magic and quite a few different utilities to get it all going, but in the end [Larry] is able to play Overwatch on max settings at a nice 60fps for $1.56 an hour. Considering that just buying the graphics card alone will set you back 2500 hours of play time, for the casual gamer, this is a great deal.

It’s interesting to see computers start to become a rentable resource. People have been attempting streaming computers for a while now, but this one is seriously impressive. With such a powerful graphics card you could use this for anything intensive, need a super high-powered video editing station for a day or two? A CAD station to make anyone jealous? Just pay a few dollars of cloud time and get to it!

Raspberry Pi, Send Me A Letter

October 4, 2016 by 20 Comments

The abundance of small networked boards running Linux — like the Raspberry Pi — is a boon for developers. It is easy enough to put a small cheap computer on the network. The fact that Linux has a lot of software is a double-edged sword. On the one hand, it is a good bet that anything you want to do has been done. On the other hand, some of the solutions are a bit large for a tiny embedded system.

Take, for example, e-mail. Historically, Linux hosts operate as mail transfer agents that can send and receive mail for all their users and possibly even relay mail to others. In today’s world, that’s usually overkill, but the capability is there. It is possible to install big mail transfer agents into a Raspberry Pi. The question is: should you?

What Do You Want?

The answer, of course, depends on what you want to do. If you have a dedicated board sending out text and maybe even files using an external mail server (like, say, Gmail), then the answer is no. You don’t need a piece of software listening for incoming connections, sorting through multiple users, and so on.

Luckily, there are some simple solutions if you know how to set up and configure them. The key is to avoid the big mail programs that do everything you don’t need.

Mail Front Ends

Let’s tackle sending mail first. If you try to grab the mailutils package, you’ll see it drags along a lot of stuff including mysql. Keep in mind, none of this will actually send mail. It just gives you some tools to get mail ready to send.

Luckily, the bsd-mailx package has a lot less overhead and will do the job. Look at the man page to see what options you have with mailx; you can do things like attach files, set a subject, and specify addresses.

It is a little difficult to set up for Gmail, though, thanks to Google’s security. You’ll need the certutil tool from the libnss3-tools package. You’ll need to create a certificate store, import Google’s certificate, and then set up a lot of options to mailx. I don’t suggest it. If you insist, though, you can find directions on the Web.

SSMTP

By default, programs like mailx and other Linux mail commands rely on a backend (often sendmail). Not only does that drag around too much overhead, it is also a full mail system, sending and receiving and relaying–overkill for our little Pi computers.

Luckily, SSMTP is available which only sends mail and is relatively lightweight. You need a configuration file to point it to your mail server. For Gmail, it would look like this:

#
# Config file for sSMTP sendmail
#
# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.
root=postmaster

# The place where the mail goes. The actual machine name is required no 
# MX records are consulted. Commonly mailhosts are named mail.domain.com
mailhub=smtp.gmail.com:587

# Where will the mail seem to come from?
rewriteDomain=yourdomain.com

# The full hostname
hostname=yourhostname
AuthUser=YourGmailUserID
AuthPass=YourGmailPassword
UseTLS=Yes
UseSTARTTLS=YES
# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
FromLineOverride=YES

You can use a mail agent like mailx or you can just use ssmtp directly:

ssmtp someone@somewhere.com

Enter a message on the standard input and end it with a Control+D (standard end of file for Linux).

Google Authentication

There’s only one catch. If you are using Gmail, you’ll find that Google wants you to use stronger authentication. If you are using two-factor (that is, Google Authenticator), this isn’t going to work at all. You’ll need to generate an app password. Even if you aren’t, you will probably need to relax Google’s fear of spammers on your account. You need to turn on the “Access for less secure apps” setting. If you don’t want to do this on your primary e-mail account, considering making an account that you only use for sending data from the Pi.

Sending Files

Depending on the mail software you use, there are a few ways you can attach a file. However, the mpack program makes it very easy:

mpack -a -s 'Data File' datafile.csv me@hackaday.com

The above command will send datafile.csv as an attachment with the subject “Data File.” Pretty simple.

Receiving Mail

What if you want to reverse the process and receive mail on the Pi? There is a program called fetchmail that can grab e-mails from an IMAP or POP3 server. It is possible to make it only read the first unread message and send it to a script or program of your choosing.

You have to build a configuration file (or use the fetchmailconf program to build it). For example, here’s a simple .fetchmailrc file:

poll imap.gmail.com
protocol IMAP
user "user@gmail.com" with password "yourpassword" mda "/home/pi/mailscript.sh"
folder 'INBOX'
fetchlimit 1
keep
ssl

You can leave the “keep” line out if you don’t mind fetchmail deleting the mail after processing. The file should be in your home directory (unless you specify with the -f option) and it needs to not be readable and writable by other users (e.g., chmod 600 .fetchmailrc). According to the fetchmail FAQ, there are some issues with Gmail, so you might want to consider some of the suggestions provided. However, for simple tasks like this, you should be able to work it all out.

In particular, the mailscript.sh file is where you can process the e-mail. You might, for example, look for certain keyword commands and take some action (perhaps replying using ssmtp).

Special Delivery

You might not think of the Raspberry Pi as an e-mail machine. However, the fact that it is a pretty vanilla Linux setup means you can use all sorts of interesting tools meant for bigger computers. You just have to know they exist.