Category Archives: Sys Admin

Material related to systems administration.

Web page HTML/CSS/JavaScript file size

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I found this article (Some Guidelines for Determining Web Page and File Size) today which talks about the average size of HTML and other files on the web. According the article (and I’m not clear how they got their data) the average HTML file is 25k, JPEG 11.9k, GIF 2.9k, PNG 14.5k, SWF 32k, external scripts 11.2k and external CSS 17k with the average total size of a web page being 130k. Interesting stuff. Particularly that scripts are typically 11.2k given that jQuery is 90k.

I’m really struggling with a design decision at the moment, being that I’m not sure whether it’s better to embed CSS/JavaScript content or to link it. The thing is that if you link it then the client has to send extra HTTP requests (at least two) to get the content, which is overhead and takes time. The thing is, if your users are returning customers then they might already have the linked files in their cache, meaning they don’t need to send extra HTTP requests, or if they do maybe those requests won’t need to return content. But then maybe a browser will cache a file when it shouldn’t (this can be avoided with good design), or maybe the user’s connection will fail while loading the linked files and they’ll see an unstyled page in their browser.

So many pros and cons, and it’s all hypothetical… what I really need is data. Anyway, I don’t have data, nor do I really have the tools to get it. So given that I have to fly in the dark, here’s my plan:

When I’m processing a request for a user who doesn’t have a browser cookie set I will embed CSS and JavaScript in the HTML. This is because if their browser cookie isn’t set then this is their first request to my web-site, maybe ever, or maybe just in a while. Either way, it’s probably safe to assume they’re a first-time visitor so they won’t have any content in their cache and they’d need to send additional requests for linked files. So I can save those additional requests and hopefully make my web pages load faster for users who are probably one-off visitors.

But for regular users having to download the same content over and over in every request gets tired fast. The linked files can be about half the size of the page, so embedding doubles the size of each transfer. When I’m processing a request if the user’s browser cookie is already set then I’ll assume they’re a regular visitor and link my JavaScript files rather than embedding them. I’ll still embed CSS content though, because my CSS content is relatively small and I want to avoid errors where the page loads but the styles don’t.

Then I’ll make the system configurable so users can change their link/embed settings for CSS and JavaScript if they’re not happy with the defaults. Regular power users can use this feature to turn on linking for all content so pages load as fast as possible for them.

crontab

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I’m setting up some backup scripts and am using cron to schedule them to run. Usually I run my backup scripts as root and just link a file into /etc/cron.*/ for periodic processing. However in this case I need to run the backup scripts as my user (they’re offsite backup scripts that use rsync to copy data) and not root, so I used crontab -e to edit my crontab. I did a little reading on crontab and learned about the @weekly syntax which I’ve used for the first time today. Now I guess I just wait a week and see that everything is working. :)

WinSCP command line options

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Finally got around to taking a look at WinSCP’s command-line options. Basically I just needed to specify a session name and that was it. Now I have a set of icons on my desktop for scping to my various servers. I even configured a shortcut key for servers I use often, so now all I need to do to get at my remote ProgClub files is press Ctrl+Alt+Shift+C.

Bash aliases for listing hidden files

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I finally figured out the ls command to list hidden files, and decided to setup a ~/.bash_aliases file for the first time. My ~/.bash_aliases file is now:

alias l.='ls -d .[!.]*'
alias ll.='ll -d .[!.]*'

So I have an “l.” command which will list hidden files and directories, and an “ll.” command which will list the same information in detail.

Keeping Your SSH Sessions Alive Through NAT Firewalls

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I found this article Keeping Your SSH Sessions Alive Through Pesky NAT Firewalls which explained how to keep SSH connections alive through NAT firewalls. I’m behind a NAT router and my SSH connections are always timing out due to inactivity, and it annoys the shit out of me. I’ve been putting up with it for ages, and tonight I finally got around to searching for a solution. The solution is to edit your ~/.ssh/config file and add:

Host *
    ServerAliveInterval 240

That will make the server send a keep-alive packet every four minutes, which out to do it. Haven’t tried it yet, but expect it will work. Will configure my systems now…

Update: that didn’t seem to work for me. :(

Maybe this is a client setting?

Anyway, I did some more research, and I found that PuTTY has a configuration option in the Connection settings “Sending of null packets to keep session active”, “Seconds between keepalives” which defaults to 0 (turned off). So I’m gonna try with that now.

Setting a default value if a bash variable is undefined

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Say you want to take an optional command line argument to your script. That means that maybe $1 is set to a value, or maybe it’s not. You can read out the value and assign a default in the case that $1 is not set using the syntax:

  variable=${1:-default-value}

Which will set $variable to “default-value” if $1 is not set.