BigSmoke » Technology

Commenting fixed for blog.bigsmoke.us

Rowan Rodrik — Sat, 04 Feb 2012 11:10:31 +0000

To my great surprise, thanks to Tobias Sjösten, I found out that commenting was broken on blog.bigsmoke.us. I couldn’t pinpoint the exact problem, but it must have been introduced with some WordPress upgrade somewhere along the line. I never noticed it because it did work for logged in users. (If I must really guess, I suspect a silent ReCaptcha version compatibility problem.)

Upgrading WordPress and wp-recaptcha to their latest versions (3.3.1 and 3.1.4 respectively) seems to have solved the problem.

MediaWiki ConfirmEdit/QuestyCaptcha extension

Rowan Rodrik — Tue, 17 Jan 2012 13:43:44 +0000

Since I moved my LDAP wiki over from DokuWiki to MediaWiki, I’ve been burried by a daily torrent of spam. Just like with my tropical timber investments wiki, the ReCaptcha extension (with pretty intrusive settings) doesn’t seem to do much to stop this shitstream.

How do the spammers do this? Do they primarily trick visitors of other websites into solving this captchas for them or do they employ spam-sweatshops in third-world countries? Fuck them! I’m trying something new.

I’ve upgraded to the ConfirmEdit extension. (ReCaptcha has also moved into this extension.) This allows me to try different Captcha types. The one I was most interested in is QuestyChaptcha, which allows me to define a set of questions which the user needs to answer. I’m now trying it out with the following question:

$wgCaptchaQuestions[] = array( 'question' => "LDAP stands for ...", 'answer' => "Lightweight Directory Access Protocol" );

I don’t think it’s a particularly good question, since it’s incredibly easy to Google. But, we’ll see, and in the mean time I’ll try to come up with one or two questions that are context-sensitive, yet easy enough to answer for anyone with some knowledge of LDAP. If you have an idea, please leave a comment.

Safari: don’t give gzipped content a .gz extension

Rowan Rodrik — Sun, 15 Jan 2012 22:39:13 +0000

Yesterday, while helping Caloe with the website for her company De Buitenkok, I came across the mother of all stupid bugs in Safari . Me having recently announced payformystay.com, I loaded it up in Apple’s hipster browser only to notice that the CSS wasn’t loaded. Oops!

Reloading didn’t help, but … going over to the development version, everything loaded just fine. Conclusion? My recent optimizations—concatenating + gzipping all javascript and css—somehow fucked up payformystay for Safari users. The 14 Safari visitors (16.28% of our small group of alpha users) I received since the sixth must have gotten a pretty bleak image of the technical abilities of payformystay.com’s Chief Technician (me).

The old `cat | gzip`

So, what happened?

To reduce the number of HTTP requests per page for all the JavaScript/CSS stuff (especially when none of it is in the browser cache yet), I made a few changes to my build file to scrape the of my layout template (layout.php), which I made to look something like this:

 if (DEV_MODE): ?>
  "stylesheet" type="text/css" href="/layout/jquery.ui.selectmenu.css" />                                   
  "stylesheet" type="text/css" href="/layout/fancybox/jquery.fancybox-1.3.4.css" />                         
  "stylesheet" type="text/css" href="/layout/style.css" />                                                  
 
                                            
                                               
                                 
                                        
                                               
                              
                                    
                               
 else: # if (!DEV_MODE) ?>
  "/layout/motherofall.css.gz?2" rel="stylesheet" type="text/css" />
  
 endif ?>

It’s very simple: All the files with a “&lt!--MERGE ME-->” comment on the same line got concatenated and gzipped into motherofall.css.gz and 3rdparty.js.gz respectively, like so:

MERGE_JS_FILES := $(shell grep '' layout/layout.php|sed -e 's/^.*

I chose to directly reference the gzipped version of the css/js, even though I had a .htaccess files in place (within /layout/) which was perfectly capable of using the right Content-Encoding for each Accept-Encoding.

`$ cat /layout/.htaccess`

AddEncoding gzip .gz
 
RewriteEngine On
 
RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteCond %{REQUEST_FILENAME}.gz -f
RewriteRule ^(.*)$ $1.gz [QSA,L]
 

ForceType text/css

 

ForceType application/javascript

You may notice that the .htaccess file contains some configuration to make sure that the .gz files are not served as something like application/gzip-compressed.

Anyway, I went to see if there were any browsers left that do not yet Accept-Encoding: gzip and could find none. When, yesterday, I was faced with an unstyled version of my homepage, my first reaction was (after the one where I was like hitting reload 20 times, embarrassedly mumbling something about “those damn browser-caches!”): “O then, apparently, Safari must be some exception to the rule that browsers have all been supporting gzip encoding for like forever!”

No, it isn’t so. Apparently Safari ignores the Content-Type header for any resource with an URL ending in .gz. Yes, that’s right. Safari understand Content-Encoding: gzip just fine. Not problems. Just don’t call it .gz.

The new `cat ; gzip`

So, let’s remove the .gz suffix from these files and be done with it. The .htaccess was already capable of instructing all necessary negotiations to be able to properly serve the gzipped version only when it’s accepted (which is always, but I digress).

A few adjustments to my Makefile:

MERGE_JS_FILES := $(shell grep '' layout/layout.php|sed -e 's/^.*

That’s it. I welcome back all 14 Safari users looking for paid work abroad! Be it that you’re looking for international work in Africa, in America, in Asia or in Europe, please come visit and have a look at what we have on offer.

Announcing payformystay.com

Rowan Rodrik — Fri, 06 Jan 2012 21:04:37 +0000

Januari the first, a very good day to announce a new project that I’ve been working on this past year. Which I did, on Facebook and Twitter. Now, five days later, it’s time te repeat the announcement to give it some much-needed link-juice. I know that normal people don’t follow this blog. (I don’t even follow this blog!) But it does have PageRank. And it does have 4000 monthly visitors. Time for some link-whoring!

PFMS search screen - top

PFMS search screen - bottom

payformystay.com is a website for adventurers who’re looking for paid work abroad. Whether you want to work in Europe, work in Afrika, work in Asia, work in Australia or whether you just want to do some seasonal work anywhere but home (grape picking, strawberry harvest, whatever you fancy). Of course we have many types of work: office jobs, tourism jobs, healthcare jobs, childcare jobs, wildlife jobs, anything.

The cool thing about payformystay, though, is that we only sport paid jobs. So, no wrestling through page after page of crappy offers where some evil cunt swine tries to make you pay for your own work. That’s right! Job offers on payformystay.com must at the very least include full board (something like a bed or tent and 3 meals daily) or enough pay to cover these basic living expenses! Offers are audited and violators are fed to the spammers.

Go get yourself a piece of the action:

payformystay.com – where people get paid to go on adventure

Peace out. End of announcement.

Have fun! Be scared! Be tough! And be safe!

Setting max memory of a Xen Dom0

halfgaar — Wed, 07 Sep 2011 08:10:41 +0000

I’ve had some issues with Xen crashing when I wanted to create a DomU for which the Dom0 had to shrink (see bug report). Therefore, it’s better to force a memory limit on the dom0. That is done with a kernel param.

Add this to /etc/default/grub:

# Start dom0 with less RAM
GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=512M"

Then run update-grub2 and reboot.

Fixing a broken Xen DomU after upgrading to Ubuntu 11.4 (Natty)

halfgaar — Fri, 02 Sep 2011 10:31:49 +0000

My Xen DomU’s that I upgraded to 11.4 no longer booted, because the xen-blkfront module is missing from the initramfs. To fix, do this when you get the initramfs prompt:

modprobe xen-blkfront
exit

Then after it’s booted:

root@ubuntu:~# echo "xen-blkfront" >> /etc/initramfs-tools/modules
root@ubuntu:~# update-initramfs -u

Source.

Also look at this post.

Fixing a Xen DomU’s grub config

halfgaar — Fri, 02 Sep 2011 10:30:36 +0000

When you use xen-create-image to bootstrap an ubuntu, it sets up a grub config file menu.lst. However, this boot config is not kept up-to-date with newer ubuntu’s because they use grub2 (which uses grub.cfg and not menu.lst). And Xen’s pygrub first looks at menu.lst, so if you have a stale file, it will always boot an old kernel.

I ‘Fixed’ it like this (a real fix I have yet to devise, but this works. Actually, I think it is a bug):

The grub hooks in Debian and Ubuntu don’t take the fact into account that the machine might be running as paravirtualized VM. Therefore, it can’t find /dev/xvda to install grub on, which it shouldn’t try. Bug reports exist about this, but it is not deemed important, it seems. The result is that the menu.lst that was created by xen-create-image is never updated and updates to the kernel are never booted.

Pygrub considers menu.lst over grub.cfg (which would give problems with upgrading to grub2). But you can also use it to your advantage. You can edit /etc/kernel-img.conf to look like this (do_symlinks = yes and no hooks):

do_symlinks = yes
relative_links = yes
do_bootloader = no
do_bootfloppy = no
do_initrd = yes
link_in_boot = no
postinst_hook =
postrm_hook   =

And then make /boot/grub/menu.lst with this:

default         0
timeout         2
 
title           Marauder
root            (hd0,0)
kernel          /vmlinuz root=/dev/xvda2 ro
initrd          /initrd.img

Then uninstall grub. This way, you always boot the new kernel.

CUPS printer driver for my HP4050

halfgaar — Wed, 17 Aug 2011 21:13:23 +0000

My HP4050 has a million different drivers to choose from. Some don’t have the maximum DPI, some don’t have other options, like selecting paper output. The one that works the best seems to be “HP LaserJet 4050 Series Postscript (recommended) (grayscale, 2-sided printing)”. However, I have no idea anymore if that came from hplip, foomatic, gutenprint, or whatever.

Converting a MySQL database from latin1 to utf8

halfgaar — Tue, 16 Aug 2011 13:49:49 +0000

mysqldump dbname > dbname_bak_before_messing_with_it.sql
mysqldump --default-character-set=latin1 --skip-set-charset dbname > dump.sql
sed -r 's/latin1/utf8/g' dump.sql > dump_utf.sql
mysql --execute="DROP DATABASE dbname; CREATE DATABASE dbname CHARACTER SET utf8 COLLATE utf8_general_ci;" 
mysql --default-character-set=utf8 dbname < dump_utf.sql

Setting up a postfix fallback MX

halfgaar — Sun, 22 May 2011 07:51:48 +0000

These are some short stepts and pointers to setup a postfix fallback MX. It does not describe postfix basics, nor how to install Mailscanner (a necessisity, because spammers like sending spam to fallback MX’s because they’re usually not as well protected).

First, postfix has a special transport, called ‘relay’, which is the same as SMTP, except that it doesn’t send to the backup MX. In this case, that means it doesn’t send to itself, avoiding loops. The relay transport is the default for all the domains you specify in the relay_domains parameter.

Should the machine have a relayhost defined, you need to disable that for each of the domains you’re a backup MX for. You can do that with transport_maps. In my case, the transport_maps is hash:/etc/postfix/transport_maps. That is a key-value file on which you run ‘postmap’ after you’ve edited it. In it, specify this (the comments explain it):

# When you specify a transport without nexthop, it resets the relay to the
# recipient domain (see man 5 transport). And, when the transport is relay,
# postfix will not relay to the backup MX, to prevent loops back to itself. So,
# because this host has a default relayhost, use the folowwing when you want to
# specify a domain for which we are backup MX: 
# example.com            relay

The next step you want to do is take measures to prevent mails to non-existent users piling up in the queue. Because spam is sent to the backup MX all the time, it will relay it to the primary, which rejects it. Your backup host will then bounce all kinds of spam mails…

To fix that, we instruct postfix to use recipient address verification. This causes it to probe the primary host to check the address exists (and caches that info) before relaying.

To enable it, do this:

smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination, reject_unknown_recipient_domain, reject_unverified_recipient
unverified_recipient_reject_reason = Address lookup failed
# Prevent caching non-existent users, to prevent delivery failures when new users are unknown still.
address_verify_negative_cache = no
# Setting to 550 to make a reject a fatal error, not a defer.
unverified_recipient_reject_code = 550
# The point of a backup MX is to accept mail when the primary is down, so setting this prevents incoming mail being deferred when the address probe cannot be done.
# TODO: find out how to actually implement it, because it doesn't work; permit it not a valid option here.
#unverified_recipient_tempfail_action = permit

The reject_unknown_recipient_domain prevents probes to domains that don’t exist.

Some extra options, not strictly related to being a backup MX:

smtpd_sender_restrictions = reject_unknown_sender_domain, reject_unknown_helo_hostname
unknown_address_reject_code = 550
# Override the default of 5 days, because the point of a backup MX is to keep it around for a while.
maximal_queue_lifetime = 21d