Friday, July 20, 2007

Essential Linux Utilities

Ever since setting up three Linux PC's in a row, I've realised that I've grown dependent on a few pieces of software for Linux, above and beyond what comes with a standard distro (or, at least, Slackware).

Beep - a tiny util that can beep the PC speaker in a variety of ways, perfect for headless systems. I use it to give a warning tones inside boot scripts and also to provide a rising or falling tone on the start or end of certain tasks, such as booting or shutting down. Because it uses the PC speaker, it doesn't interfere with ALSA, works on even the oldest of PC's, doesn't necessarily require an external set of speakers etc. Beware using it, however, on multi-user installations - I tend to keep it restricted to the audio group of users only to stop people messing about with it.

Ether-wake (available from various places, originally by Donald Becker) - the ultimate power-saving util... this is a Wake-on-LAN packet broadcaster to wake up computers that support WoL from their deep sleep (i.e. turn them on so long as they are plugged into the net and have a power cable in them). With this I keep my home network largely turned off and "wake up" (i.e. turn on) particular PC's as and when I need them. And larger scale experiments have shown that there's nothing better than the sound of a room full of PC's all booting up simultaneously at the click of a single button / cron job.

HTop - a better version of "top" that I find easier to use. Shows processes and RAM usage in a nice controllable text-mode GUI that allows you to kill individual processes, scroll up and down etc.

rc.firewall (See this post for a mirror) - a perfect, simple, one-file iptables firewall that works well as rc.firewall in Slackware. Works for single computers, NAT'ing routers, multiple network cards, multiple-networks-on-a-single-card, and lots of other configurations. It uses a simple syntax for even multi-port port-forwards, has many simple options for various things such as allowing or deny ping's or cross-network traffic, has a very strong default configuration and can be reloaded at the drop of a hat at which point all the detected network interfaces are re-firewalled.

x11vnc - This is one of those utilities that few people ever use. It's a vnc server for X. But it has a vital difference... it's a VNC server for EXISTING X sessions. Most people are familiar with xVNC which allows you to spawn an entire X-Windows system where each "screen" is actually a VNC session (thereby providing instant-VNC-thin-client) but that's not much use to someone that has a single-user Linux PC who wants to log onto their home PC and click on that link that they left showing in their browser. x11VNC does just that - the command-lines get horrid very quickly, you have to pay close attention to the security of the thing (because now connecting to the PC on port 5900 is the equivalent of logging in as yourself on the local PC!) but it's a great piece of software. The author is also working hard to make VNC-wrapped-in-SSH a cinch, even from Windows PC's, by extending the TightVNC clients to incorporate SSL tunnelling. Yeah, you can now do this with some things like KDE's Remote Desktop functionality but I've been using this particular utility for so long that I have scripts which build-on to it and it also has some features that just aren't present in other imitators.

knockd - a simple port-knocking daemon implementation which can be triggered remotely using either a tiny utility that works on Linux/Unix/Windows or by simpler tools such as telnet. Perfect for securing a server for remote access (and incidentally the best way to stop random port probes to your machine - my SSH logs were filling up until I found this) as you can just put the portknock client on a usb disk or a website and download it from wherever you happen to be or you can even "bodge" one in a real emergency. Also, the configuration basically consists of port-sequences and names of scripts to run. This means that it's easy to configure it to see port-hits on ports X,Y,Z as an instruction to run an "open" script and then you can hit ports Z,Y,X to run a "close" script. And because you can have multiple port sequences running, it's very easy to have all sorts of different things happening. See my article here for a bit more background on my use of this utility.

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