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Running Prolog on Linux

The learning prolog banner. Hello! I hope you had a nice restful Easter. I've been a bit busy this last 6 months, but I've got a holiday at the moment, and I've just received a lovely email about my learning prolog series. It's reminded me about how much I actually rather like (swi) prolog (I'm a bit nuts, I know :P), and I've decided that it would be splendid if I could get back into it a bit.

I'm not sure whether it'll go anywhere, but I'm going to look into web crawling and parsing HTML. Anyway, since I'm re-discovering prolog, I had a teensy bit of trouble getting prolog to run one of my old scripts just now, so I thought I'd blog about it to save me the trouble next time :D

Running prolog scripts on linux isn't actually that hard. First, you need to install SWI-Prolog:

sudo add-apt-repository ppa:swi-prolog/stable
sudo apt install swi-prolog-nox

Then, you run a prolog script like this:

swipl -f ./Awesome-Prolog.pl
Welcome to SWI-Prolog (threaded, 64 bits, version 7.4.1)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit http://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- 

...then you can interact with your Prolog knowledge bases as normal. When you want to exit, the easiest way I've found is if you press CTRL + D.

If, however, you're lazy and don't want to type prolog -f AwesomeSauce.pl out every time you want to run your script, you can prefix your file with the following shebang:

#!/usr/bin/prolog -f 

Make sure it's the very first line in the file. Prolog appears to ignore it and carry on regardless. Then you can run it like this (making sure you've chmod +x'd it first:

./CoolBot.pl

Profiling PHP with XDebug

(This post is a fork of a draft version of a tutorial / guide originally written as a whilst at my internship.)

The PHP and xdebug logos.

Since I've been looking into xdebug's profiling function recently, I've just been tasked with writing up a guide on how to set it up and use it, from start to finish - and I thought I'd share it here.

While I've written about xdebug before in my An easier way to debug PHP post, I didn't end up covering the profiling function - I had difficulty getting it to work properly. I've managed to get it working now - this post documents how I did it. While this is written for a standard Debian server, the instructions can easily be applied to other servers.

For the uninitiated, xdebug is an extension to PHP that aids in the debugging of PHP code. It consists of 2 parts: The php extension on the server, and a client built into your editor. With these 2 parts, you can create breakpoints, step through code and more - though these functions are not the focus of this post.

To start off, you need to install xdebug. SSH into your web server with a sudo-capable account (or just use root, though that's bad practice!), and run the following command:

sudo apt install php-debug

Windows users will need to download it from here and put it in their PHP extension direction. Users of other linux distributions and windows may need to enable xdebug in their php.ini file manually (windows users will need extension=xdebug.dll; linux systems use extension=xdebug.so instead).

Once done, xdebug should be loaded and working correctly. You can verify this by looking the php information page. To see this page, put the following in a php file and request it in your browser:

<?php
phpinfo();
?>

If it's been enabled correctly, you should see something like this somewhere on the resulting page:

Part of the php information page, showing the xdebug section.

With xdebug setup, we can now begin configuring it. Xdebug gets configured in php.ini, PHP's main configuration file. Under Virtualmin each user has their own php.ini because PHP is loaded via CGI, and it's usually located at ~/etc/php.ini. To find it on your system, check the php information page as described above - there should be a row with the name "Loaded Configuration File":

The 'loaded configuration file' directive on the php information page.

Once you've located your php.ini file, open it in your favourite editor (or type sensible-editor php.ini if you want to edit over SSH), and put something like this at the bottom:

[xdebug]
xdebug.remote_enable=1
xdebug.remote_connect_back=1
xdebug.remote_port=9000
xdebug.remote_handler=dbgp
xdebug.remote_mode=req
xdebug.remote_autostart=true

xdebug.profiler_enable=false
xdebug.profiler_enable_trigger=true
xdebug.profiler_enable_trigger_value=ZaoEtlWj50cWbBOCcbtlba04Fj
xdebug.profiler_output_dir=/tmp
xdebug.profiler_output_name=php.profile.%p-%u

Obviously, you'll want to customise the above. The xdebug.profiler_enable_trigger_value directive defines a secret key we'll use later to turn profiling on. If nothing else, make sure you change this! Profiling slows everything down a lot, and could easily bring your whole server down if this secret key falls into the wrong hands (that said, simply having xdebug loaded in the first place slows things down too, even if you're not using it - so you may want to set up a separate server for development work that has xdebug installed if you haven't already). If you're not sure on what to set it to, here's a bit of bash I used to generate my random password:

dd if=/dev/urandom bs=8 count=4 status=none | base64 |  tr -d '=' | tr '+/' '-_'

The xdebug.profiler_output_dir lets you change the folder that xdebug saves the profiling output files to - make sure that the folder you specify here is writable by the user that PHP is executing as. If you've got a lot of profiling to do, you may want to consider changing the output filename, since xdebug uses a rather unhelpful filename by default. The property you want to change here is xdebug.profiler_output_name - and it supports a number of special % substitutions, which are documented here. I can recommend something phpprofile.%t-%u.%p-%H.%R.%cachegrind - it includes a timestamp and the request uri for identification purposes, while still sorting chronologically. Remember that xdebug will overwrite the output file if you don't include something that differentiates it from request to request!

With the configuration done, we can now move on to actually profiling something :D This is actually quite simple. Simply add the XDEBUG_PROFILE GET (or POST!) parameter to the url that you want to test in your browser. Here are some examples:

https://localhost/carrots/moon-iter.php?XDEBUG_PROFILE=ZaoEtlWj50cWbBOCcbtlba04Fj
https://development.galacticaubergine.de/register?vegetable=yes&mode=plus&XDEBUG_PROFILE=ZaoEtlWj50cWbBOCcbtlba04Fj

Adding this parameter to a request will cause xdebug to profile that request, and spit out a cachegrind file according to the settings we configured above. This file can then be analysed in your favourite editor, or, if it doesn't have support, an external program like qcachegrind (Windows) or kcachegrind (Everyone else).

If you need to profile just a single AJAX request or similar, most browsers' developer tools let you copy a request as a curl or wget command (Chromium-based browsers, Firefox - has an 'edit and resend' option), allowing you to resend the request with the XDEBUG_PROFILE GET parameter.

If you need to profile everything - including all subrequests (only those that pass through PHP, of course) - then you can set the XDEBUG_PROFILE parameter as a cookie instead, and it will cause profiling to be enabled for everything on the domain you set it on. Here's a [bookmarklet]() that set the cookie:

javascript:(function(){document.cookie='XDEBUG_PROFILE='+'insert_secret_key_here'+';expires=Mon, 05 Jul 2100 00:00:00 GMT;path=/;';})();

(Source)

Replace insert_secret_key_here with the secret key you created for the xdebug.profiler_enable_trigger_value property in your php.ini file above, create a new bookmark in your browser, paste it in (making sure that your browser doesn't auto-remove the javascript: at the beginning), and then click on it when you want to enable profiling.

Was this helpful? Got any questions? Let me know in the comments below!

Sources and further reading

My new Raspberry Pi 3!

My new Raspberry Pi 3!

I've got a little project in mind - I'd like to build a little storage server to back some things up to. It doesn't have to be anything terribly fancy, provide blisteringly fast speeds, or have store a huge number of files, so I've opted for a Raspberry Pi 3 to power the thing. It arrived just recently, and since the service I got from Pimoroni was excellent, I thought I'd post about it here. If you're after some bits for your raspberry pi, then they are a good reputable place to get them from.

In order to access the storage space on the server, I'll be configuring some samba shares (linux's implementation of Windows file shares, which is completely interoperable). Would anyone be interested in a tutorially kind of post on how you configure Samba? Let me know in the comments below.

Website Integrations #2: oEmbed

Welcome to part 2 of this impromptu miniseries! In this second part of three, I'll be showing you a little about how I set up and tested a simple oEmbed provider for my blog posts - I've seen lots of oEmbed client information out there, but not much in the way of provider (or server) implementations.

If you haven't read part one about the open graph protocol yet, then you might find it interesting.

oEmbed is a bit different to open graph in that instead of throwing a bunch of meta tags into your <head />, you instead use a special <link /> element that points interested parties in the direction of some nice tasty json. Personally, I find this approach to be more sensible and easier to handle - the kind of thing you'd expect from an open standard.

To start with, I took a read of their specification, as I did with open graph. It doesn't have as many examples as I'd have liked, and I had to keep jumping around, but it's certainly not the worst I've seen.

oEmbed is built on the idea of providers (that's me!) and consumers (the programs and website you use). Providers, erm, provide machine-readable information about urls passed to them, and consumers take this information provided to them and display it to the user in a manner they think is appropriate.

To start with, I created a new PHP file to act as my provider over at https://starbeamrainbowlabs.com/blog/oembed.php and took a look at the different oEmbed types available - oEmbed has a type system of sorts, similar to open graph. I decided on link - while a rich would look cool, it would be almost impossible to test with every client out there, and I can't guarantee how the html would be rendered or what space it would have either.

With that decided, I made a list of the properties that I'd need to include in the json response:

  • version - The version of oEmbed. Currently 1.0 as of the time of typing.
  • type - The oEmbed type. I chose link here.
  • title - The title of the page
  • author_name - The name of the author
  • author_url - A link to the author's homepage.
  • provider_name - The provider's name.
  • provider_url - A link to the provider's homepage. I chose my blog index, since this script will only serve my blog.
  • cache_age - How long consumers should cache the response for. I put 1 hour (3600 seconds) here, since I usually correct mistakes after posting that I've missed, and I want them to go out fairly quickly.
  • thumbnail_url - A link to a suitable thumbnail picture.
  • thumbnail_width - The width of the thumbnail image, in pixels.
  • thumbnail_height - The width of the thumbnail image, in pixels.

Then I looked at the data I'd be getting from the client. It all comes in the form of GET parameters:

  • format - Either json or xml. Personally, I only support json.
  • url - The url to send oEmbed information for.

With all the information close at hand, I spent a happy hour or so writing code, and ended up with a script that outputs something like this:

{
    "version": "1.0",
    "type": "link",
    "title": "Website Integrations #1: Open Graph",
    "author_name": "Starbeamrainbowlabs",
    "author_url": "https:\/\/starbeamrainbowlabs.com\/",
    "provider_name": "Stardust | Starbeamrainbowlabs' Blog",
    "provider_url": "https:\/\/starbeamrainbowlabs.com\/blog\/",
    "cache_age": 3600,
    "thumbnail_url": "https:\/\/starbeamrainbowlabs.com\/images\/logos\/open-graph.png",
    "thumbnail_width": 300,
    "thumbnail_height": 300
}

(See it for yourself!)

Though the specification includes requirements for satisfying 2 extra GET parameters, maxwidth and maxheight, I chose to ignore them since writing a dynamic thumbnail rescaling script is both rather complicated and requires a not insignificant amount of processing power every time it is used.

After finishing the oEmbed script, I turned my attention to one final detail: The special <link /> tag required for auto-discovery. A quick bit of PHP in the article page renderer adds something like this to the header:

<link rel="alternate" type="application/json+oembed" href="https://starbeamrainbowlabs.com/blog/oembed.php?format=json&url=https%3A%2F%2Fstarbeamrainbowlabs.com%2Fblog%2Farticle.php%3Farticle%3Dposts%252F229-Website-Integrations-1-Open-Graph.html" />

and with that, my oEmbed provider implementation is complete - but it still needs testing! Unfortunately, testing tool for oEmbed are few and far between, but I did manage to find a few:

  • oEmbed Tester - A basic testing tool. Appears to work well for the most part - except the preview. Not sure why it says "Preview not available." all the time.
  • Iframely URL Debugger - Actually a testing tool for some commercial tool or other, but it still appears to accurately test not only oEmbed, but open graph and twitter cards (more on them in the next post!) too!

After testing and fixing a few bugs, my oEmbed provider was complete! Next time, I'll be taking a look at twitter's take on the subject: Twitter cards.

Found this interesting? Comment below! Share it with a friend!

Website Integrations #1: Open Graph

The logo of the Open Graph protocol.

These days, if you share a link to a website or a blog post with a friend or on a social networking site, sometimes the link expands to a preview of the link you've just posted. Personally, I find this behaviour to be quite helpful, as it lets me get an idea as to what it is that I'm about to click on.

Unfortunately, when it comes to the code behind these previews, there are no less than 3(!) different protocols that you need to implement in order to get it to work, since facebook, twitter, and the rest of the web community haven't been talking to each other quite like they should have been.

Anyway, after implementing these 3 protocols and having a bit of trouble with them, I thought I'd write up a mini-series on the process I went through, the problems I encountered, and how I solved them. In this post, I'm going to explain Facebook's Open Graph protocol.

I decided that I'd implement these 3 protocols on my home page and each blog post's page. Open Graph was the easiest - all it requires is a bunch of meta tags. These tags are split into 2 parts - the common tags, which all page types should have, and the type-specific tags, which depend on the type of page you're implementing them on. Here's the list of common tags I implemented:

  • og:title - The title of your page
  • og:description - A short description of your page
  • og:image, og:image:url, and og:image:secure_url - The url of an image that would fit as a preview for the page
  • og:url - The url of the page (not sure why this is required, since you have to know the url in order to require the page... :P Perhaps it's to help with deduplication - I'm not sure)

These were fairly easy for my home page:

<meta property="og:title" content="Starbeamrainbowlabs" />
<meta property="og:description" content="Hi! I am a computer science student who is in their second year at Hull University. I started out teaching myself about various web technologies, and then I managed to get a place at University, where I am now." />
<meta property="og:image" content="http://starbeamrainbowlabs.com/favicon.png" />
<meta property="og:image:url" content="http://starbeamrainbowlabs.com/favicon.png" />
<meta property="og:image:secure_url" content="https://starbeamrainbowlabs.com/favicon.png" />
<meta property="og:url" content="https://starbeamrainbowlabs.com/" />

When I went to test it using Facebook's official testing tool, the biggest problem I had was that the image wouldn't show up - no matter what I did. I eventually found this stackoverflow answer which explained that Facebook doesn't support https urls in anything other than the og:image:secure_url meta tag (even though they say they do) - so changing the urls to regular http solved the problem.

Next, I took a look at the type-specific tags. There's a whole bunch of them (check out this section of the spec) - I decided on the profile type for the index page of my website here:

<meta property="og:type" content="profile" />

The profile type has a few extra specific meta tags that need setting too, so I added those:

<meta property="profile:first_name" content="Starbeamrainbowlabs" />
<meta property="profile:last_name" content="Tjovik" />
<meta property="profile:username" content="Starbeamrainbowlabs" />

With that done, I turned my attention to my blog posts. Since the page is rendered in PHP (and typing out all those meta tags was a rather annoying), I created a teensy little framework to output the meta tags for me

$metaTags = [];
$metaTags["property"] = "value";

$renderedMetaTags = "";
foreach($metaTags as $metaKey => $metaValue)
    $renderedMetaTags .= "\t<meta property=\"$metaKey\" content=\"$metaValue\" />";

Now I can add as many meta tags as I like, with a fraction of the typing - and it looks neater too :D With that done, I implemented the basic meta tags. Here's some example output from the last post:

<meta property="og:title" content="4287 Reasons why your comments weren't posted" />
<meta property="og:description" content="I don't get a lot of real comments on here from what I can tell, as you've probably noticed. I don't particularly mind (though it's always awesome whe.... (click to read more)" />
<meta property="og:image" content="http://starbeamrainbowlabs.com/blog/images/20170406-Spammer-Mistakes.png" />
<meta property="og:image:url" content="http://starbeamrainbowlabs.com/blog/images/20170406-Spammer-Mistakes.png" />
<meta property="og:image:secure_url" content="https://starbeamrainbowlabs.com/blog/images/20170406-Spammer-Mistakes.png" />
<meta property="og:url" content="https://starbeamrainbowlabs.com/blog/article.php?article=posts%2F228-4287-Reasons-Your-Comments-Were-Not-Posted.html" />

That wasn't too tough. Next, I looked at the list of types again, and chose the article type for my blog posts.

<meta property="og:type" content="article" />

Like the profile type earlier, the article type also comes with a few type-specific meta tags (what they mean by not fitting into a 'vertical' I have no idea). I decided not to implement all the type-specific meta tags available here, since not all of them were practical to implement. Here's some more example output for the new tags:

<meta property="article:author" content="https://starbeamrainbowlabs.com/" />
<meta property="article:published_time" content="2017-04-08T12:56:46+01:00" />

Unfortunately, the article published time is really awkward to get hold of actually (even though it's outputted at the bottom of every article) , so I went with the 'last modified' time instead. The published time is marked up with html microdata Hopefully it doesn't cause too many issues later - though I can always change it :P

With that (and a final test), it looked like my Open Graph implementation was working as intended. Next time, I'll show you how I implemented a simple oEmbed provider.

Useful Links

4287 Reasons why your comments weren't posted

I don't get a lot of real comments on here from what I can tell, as you've probably noticed. I don't particularly mind (though it's always awesome when I do get one!) - but what I do mind about is the spam. Since February 2015, I've gotten 4287 spam comments. 4287! It's actually quite silly, when you think about it.

The other day I was fiddling with the code behind this blog (posts about that coming soon!), and I discovered that I implemented a log ages ago that records each and every spammer, and the mistake they made - and I thought I'd share some statistics here, and some tips for dealing with spam yourself (I've posted about tactics before here.

Here's an extract from my logs (full logs available on request):

[ Sun, 02 Apr 2017 23:17:25 +0100] invalid comment | ip: 94.181.153.194 | name: ghkkll | articlepath: posts/120-Cpu-Registers.html | mistake: shortcomment
[ Mon, 03 Apr 2017 02:16:58 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:58 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:59 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey
[ Mon, 03 Apr 2017 02:16:59 +0100] invalid comment | ip: 191.96.242.17 | name: exercise pants | articlepath: posts/010-Gif-Renderer.html | mistake: invalidkey

Since the output format I chose is nice and regular, I could use a quick bit of bash magic to whip up some statistics:

cat failedcomments.log | sed -e 's/^.*mistake\: //' | grep -iv '\[' | sort | uniq -c | sort -nr

(explanation, courtesy of explainshell.com )

That gave me this output:

Count Reason
3922 invalidkey
148 website
67 nokey
67 noarticleid
56 noname
17 shortcomment
4 badarticlepath
3 longcomment
2 invalidemail
1 shortname

My first thoughts here were firstly along the lines of "wow, that's a lot of spam", secondly "that comment key is working really well!", and thirdly "I didn't realise how helpful that fake website field is". Still, though I had a table, I thought a visualisation might help to put things into perspective.

A pair of pie charts showing a breakdown on which mimstakes spammers made most often. Explained below.

There - much better :D As you might have suspected if you've been following my blog here for a while, having an invalid comment key is the most common mistake spammers make.

The comment key is a hidden field in the comment form that is actually a transformed timestamp of the time you loaded the page. Working it backwards, I can work out how long it took you to submit a comment from first loading the page.

Using a companion log file to the one that I generated the above pie chart from, I've calculated that 3558 potential comments were submitted within 10 seconds of loading the page! No ordinary humans are that fast.... (especially considering you probably want to read the article before commenting!) they have to be bots. Here's a graph to illustrate the dropoff (the time is in seconds):

A graph illustrating how many bots commented on my blog unnaturally fast.

Out of the other reasons that people failed, "website" was the second most common mistake, with ~3.45% of spammers getting caught out on it. This mistake refers to another of my little spam traps - defense in depth is always good! This particular one is a regular website address hidden field, which is hidden via some fancy CSS. Curious, I decided to investigate further - and what I found was fascinating.

About 497 spammers entered an invalid website address (i.e. one that doesn't start with http) into the website box - which I really can't understand, since it's got a (hidden) label and an appropriate name and type to match - 90 of which decided that "seo plugin" was a brilliant thing to fill it with! It's important to note here that spammers who got caught by the invalid comment key filter above are included in these statistics - here's the bash command I used here:

grep -i '"website"' rawsubmits.jsonlog  | sed -e 's/^.*"website": "//' -e 's/",//' -e 's/\\\///' | uniq | egrep -iv '^http' | wc -l

Other examples include "watch live sports free", "Samantha", "just click the following web site", long strings of html-encoded unicode characters (japanese I think, after decoding one), and more. Perfectly baffling, if you ask me (if you can shed some light on this one, please comment below!).

57 spambots forgot their own name. This could be because the box you put your name in below has a name of 'name', but an id of 'namebox' - which may have caused some confusion for some of the more stupid bots.

After all that, there were 3 long comments (probably a bunch of word salad), 2 invalid email addresses that weren't caught by any filters above, and 1 short name (under 3 characters).

That's about it for this impromptu analysis of my comments log! This took far longer than I thought it would to type up. Did you find it interesting? Thinking of putting some of these techniques into practice yourself? Comment below!

Signing email with GPG/PGP in Evolution

Recently I've moved to a new laptop, and for the longest time I haven't been able to figure out why I couldn't sign my messages with gpg any more (I'm on keybase as sbrl). Turns out the problem was that gpg didn't 'trust' my private key. This post documents how I fixed it:


# First, import your private key into gpg (you've probably done this already)
gpg --import <secret_key.priv
# Then, get gpg to edit your private key, and ask it to trust your private key
gpg --edit-key toaster5@waffletoast.net
> trust
> 5
> y

Once done, you can then select your private key in evolution in the preferences (SHIFT + CTRL + S).

Did this help you out? Still having issues? Let me know in the comments below!

zram: A seriously cool way to do more with your ram

Got memory issues? Keep running out of ram? Want to store a ridiculously large file in ram because your disk (or network) is slow? If you're running linux, then look no further than zram - a hidden gem available since 3.14.

It's a little bit underdocumented, but thankfully easy to figure out, so I'm gathering everything I can find about it into one place.

zram is a kernel module for linux version 3.14 and above that allows you to use a portion of your ram to create virtual block devices (like /dev/sda1 or /dev/sdb3 for example) that actually compress data you put on them and store it in ram. It's installed by default (at least in ubuntu 16.10!) - just not enabled - so you should already have access to it if you're running a fairly recent kernel.

To start using it, you first have to enable it and load it into your running kernel. Despite how dangerous that might sound, it's actually quite safe (I think :P). Obviously, you'll need sudo (or 'Administrator' for Windows fans) privileges to do this - and if you want it to persist across reboots, you'll have to edit some file like /etc/rc.local or similar (though writing an init.d/upstart/system script/service file would probably be a better way to do it).

Here's the command to load the require kernel module:

sudo modprobe zram num_devices=2

In the above, I load the zram kernel module, and tell it to create 2 virtual devices - /dev/zram0 and /dev/zram1 (why it's called modprobe when it actually loads the module I have no idea). You can have as many devices as you want here - they don't do anything until they are initialised.

Next, as you may have guessed, you need to initialise one of the new virtual devices in order to use it. That's fairly easy too:

sudo zramctl --find --streams 2 --size 2GB --algorithm lz4

I've specified a few more options here, so I'll go through them in turn.

  • --find - This tells it to use the next available and uninitialised device. It'll echo the path to the device it ended up using to your terminal once it's done initialising.
  • --streams 2 - Sets the number of compression streams the device has. I'd recommend setting this to something around the number of cpu cores you have.
  • --size 2GB - Here I tell it the size of the virtual disk I want it to create. At most the device will use this amount of memory. I've specified 2GB here, but you should allocate a different amount based on your available ram - KB and MB are supported as suffixes here too.
  • --algorithm lz4 - This is the compression algorithm I told it to use. Currently it only supports 'lzo' and 'lz4' - I'm not sure which one is better. If you do, let me know in the comments :-)

Now that the zram device is all initialised, we can start doing things with it! Need a place to put a few files? Try this command:

sudo mke2fs -t ext4 -O ^has_journal -L "zram device" /dev/zram0

In the above I format /dev/zram0 to an ext4 partition. Note that I also disable journaling - journaling is system that ensures integrity in the event of an unplanned shutdown or loss of power - great for persistent drives like the one holding your operating system, but not so useful for one that'll get deleted automatically on shutdown anyway :-)

Perhaps you need a bit of extra speedy swap space because you don't have quite enough ram? That's easy too:

sudo mkswap --label 'zram swap parition' /dev/zram0
sudo swapon --priority 10 /dev/zram0
swapon

In the above I format /dev/zram0 to be a swap partition, and then turn it on. The final command lists the current swap devices that are currently active. You can learn more about swap partitions here.

That concludes this post. Got any cool uses for this? Found something I've missed? Write a comment below!

Sources and further reading

The HTTPS version of my website is insecure? Nonsense!

A chrome privacy warning.

I'm still rather ill, but I wanted to post about an issue I've just had with my website. Upon visiting my website in the latest version of chrome beta (57 as of the time of typing), I discovered that chrome had decided that the connection was 'insecure'. It didn't tell me precisely what the problem was (even in the developer tools :-) - why would I possibly need to know that? - only that it considered it insecure.

After googling around a bit, I didn't find any specific articles on the subject - their recent move to start considering regular http connections insecure is swamping all the relevant articles in the search results I suspect.

The big clue came when I discovered that one of my subdomains that uses a letsencrypt works as expected. You see, the main website actually used a StartSSL certificate. My running theory is that even though my certificate was an SHA2 cerrtificate, chrome decided that it was not trustworthy as there was an SHA1 certificate in the trust chain somewhere.

The fix: Replace all my existing StartSSL certificates with Let's Encrypt ones. It seems to have fixed the issue for now. I also discovered that Let's Encrypt certificates can also be used in mail servers (i.e. SMTP and IMAP) too - so I don't have to go and fiddle about with finding an alternative certificate provider.

In future, it would certainly be helpful if Google actually told people precisely what they were going to do before they do it....!

Was this useful? Could it be improved? Would you like a Let's encrypt tutorial? Let me know in the comments below!

Learning Prolog Series List

The new Learning Prolog banner!

I'm rather ill at the moment, but I had the idea of creating a banner for the Learning Prolog series I did a while ago, and at the same time I ended up realising that I never posted a full series list for it. This banner has been something to occupy my mind with while I recover, at least.

Anyway, here's the series list:

Art by Mythdael