I'm using a hosts file for ad blocking however this big (2.5mb uncompressed) file seems to lag and slow down the system with anything to do with the internet. It will even lag the network control panel and will stop the modem from dialing on startup. Is there anyway to stop this?

Also is there anyway to manually flush the DNS cache?

I think you may be going about this in a suboptimal way.

A 2.5 MB hosts file is not something common! It's definitely going to slow you down.

I'd suggest using ad blocking in the browser.

Switch to Firefox, if you haven't already done so, and download the adblock plugin.

Then when you want to block an ad, replace most of the url - the long bit after the main address - with a * to block all other ads from the same source.

Flash ads are a little more difficult, you'll need to look at the list of blockable items and work out which ones are the ads.

Don't forget to delete or drastically reduce the hosts file.

I don't know about flushing the DNS cache, sorry.

The hosts file works for opera, thunderbird, evolution to. It also acts as a way to block ads to the rest of the lan, which is using it as a NAT box. And yeah I do realise 2.5mb is a bit uncommon but hell, IT WORKS okay on windohs which makes it scary that linux doesn't!

Well, it works on Linux too but is slowing you down, possibly because linux reads it more often.

In your shoes I'd try and set up a ramdisc, copy hosts to it and replace /etc/hosts by a symlink to the new hosts file. See if this speeds things up.

I gave up on filtering on the gateway, especially when I converted the whole house to firefox - 5 people, each with different surfing habits.