Archive for February, 2010
February 27, 2010 at 6:36 pm · Filed under Linux
I’ve only recently stumbled across this, but you can now (and probably have been able to since god knows what kernel 
) use a swap file instead of having to create a swap partition. There’s no performance impact, and it’s easy to setup/configure.
Enter the following at the CLI:
#> dd if=/dev/zero of=/opt/512MB.swap bs=1M count=512
#> mkswap /opt/512MB.swap
#> swapon /opt/512MB.swap
Obviously you can put the file wherever you want. The real benefit of utilising a swap file rather than a swap partition may already be obvious: if you want to increase your swap size, simply swapoff, create a new, bigger file – and swapon again.
February 26, 2010 at 7:22 pm · Filed under BASH, Linux
If like me you use history extensively, then you’ve probably been annoyed at the fact that it forgets that complicated command from six months previous due to its size limitations.
Increasing the size of your history is an easy change, simply edit ~/.bashrc and insert the following line:
export HISTSIZE=10000
(Set HISTSIZE=0 if you want to disable the history all together).
As is already documented over at the ‘Linux Quick Tips‘ section, perhaps one of the most useful BASH shortcuts is the CTRL-R command, that allows you to search through the command history.
Also, it’s probably a good idea to stop duplicate lines from being entered one after another and taking needless space, so uncomment the following line to leave it as shown:
export HISTCONTROL=ignoredups
If you’re privacy conscious – you can change that line to read:
export HISTCONTROL=ignoreboth
That (and indeed having HISTCONTROL=ignorespace) will mean that any lines starting with a space will be ignored.
Whilst you’re in that file, you can also fix one of my pet hates when using BASH on other people’s servers – auto-completion features for programs that can use them, i.e. apt-get. If you’re logged in as a normal user, auto-completion for apt-get et al is already enabled. But for root, it isn’t.
To enable auto-completion, scroll to the bottom of the file and uncomment the appropriate section so it looks like the following:
if [ -f /etc/bash_completion ]; then
. /etc/bash_completion
fi
Finally, once you’ve saved and quitted vi/nano/vim/pico etc, to apply all the changes in your current shell, you can respawn bash by doing:
#> bash
#>
February 21, 2010 at 3:13 pm · Filed under Linux, Mailadmin
If you’re getting the following (non-)error in your log files (/var/log/mail.log), then there’s a quick way to fix it if you’re not interested in ignoring it:
Feb 21 13:57:53 zivi cyrus/imaps[4648]: SQUAT failed to open index file
Feb 21 13:57:53 zivi cyrus/imaps[4648]: SQUAT failed
The error is caused by a user doing a search within a mailbox, and a squatter file (aka a search index) is not available. Fix this by running the following as your cyrus user (typically ‘cyrus’):
#> squatter -r user.username
If you’re doing a tail -f of /var/log/mail.log you’ll see the indexes being created.
Et voila – no more errors:
Feb 21 14:10:11 zivi cyrus/imaps[5073]: SQUAT returned 277 messages
If you want to take it a step further, you can automate this by creating a cronjob. Or if you’re using a standard Cyrus installation, the last few lines of your /etc/cyrus.conf will have some useful settings commented out that will allow Cyrus to schedule the SQUAT operations automatically:
# reindex changed mailboxes (fulltext) approximately every other hour
#squatter_1 cmd=”/usr/bin/nice -n 19 /usr/sbin/squatter -s” period=120
# reindex all mailboxes (fulltext) daily
#squatter_a cmd=”/usr/sbin/squatter” at=0517
As hinted at the beginning of this entry, this is a sort of non-error in as much as it can be safely ignored, and squat indexes need only be created if their is an advantage to doing so (that is, searches are often carried out).
February 7, 2010 at 5:11 pm · Filed under Uncategorized
I’ve been working on a website for the past few weeks, and as I’m reaching the final stages I’ve started to look at loading times and performance etc. The site uses quite a lot of jQuery and other AJAX libraries, but I was still shocked when I realised that over 500kB was being used just in Javascript!
Whilst the vast majority of the population are probably now on broadband, even I can’t forgive the homepage of this website totalling almost a 1MB download when images and the rafts of CSS are included.
So I’ve been making good use of YSlow, the excellent performance debugger produced by Yahoo, which runs within Firefox (as part of the excellent Firebug suite).
My initial score was as bad as I thought, with the index page receiving a ‘Grade E’. My first port of call was to fix the GZip compression on my Apache box, which involved putting the following in a .htaccess file in the root web directory (/var/www on my Ubuntu server).
# Below uses mod_deflate to compress text files. Never compress binary files.
AddOutputFilterByType DEFLATE text/html text/plain text/css text/javascript text/xml image/svg+xml application/javascript application/x-javascript application/atom_xml application/rss+xml application/xml ap$
# Properly handle old browsers that do not support compression
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
# Explicitly exclude binary files from compression just in case
SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.(?:exe|t?gz|zip|bz2|sit|rar)$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.pdf$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.avi$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.mov$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.mp3$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.mp4$ no-gzip dont-vary
SetEnvIfNoCase Request_URI \.rm$ no-gzip dont-vary
YSlow also complained that none of the page elements had expiry headers. Expiry headers are used by the browser in order know how long to cache an object for.
First of all, enable mod_expires:
#> a2enmod expires
And then put the following in your httpd.conf (/etc/apache2/httpd.conf):
ExpiresActive on
ExpiresDefault "access plus 1 year"
You should be able to see that the above sets the expiry headers for the most common file formats, and sets them for one year in the future. You can modify this value as per your requirements, but be warned that YSlow complains if it isn’t “too far in the future”.
Finally, YSlow was complaining about ETags. ETags are explained thoroughly here, which can be summarised with: the majority of browsers use the “Last modified” header tag to validate components, and as such, ETags are largely redundant and as such they’re best turned off.
To do so, first enable mod_headers:
#> a2enmod headers
And then place the following in your site config file (i.e. /etc/apache2/sites-enabled/sitename):
ServerAdmin lm@nothingbutreboots.com
ServerName nothingbutreboots.com
ServerAlias www.nothingbutreboots.com
DocumentRoot /var/www
Options FollowSymLinks
AllowOverride All
Header unset Etag
FileETag none
Finally, all that was left to do was follow the remaining tips offered by YSlow, namely merge all the JScripts into one file, the same for CSS. And then run all the images through the excellent Smush.It.
Et voila! Grade: A 
Google now offers there own performance analysis tool: Google Page Speed. Like YSlow, it tags on to the Firebug backend. Initial reports are mixed, but there’s a helpful comparison of both tools here.
