Varilight dimmer remote control

Got one of these things a while back - they're neat dimmer switches with a touch control - no moving parts - get 'em from Homebase etc. They're remotely controllable (over IR-InfraRed) - and you can buy a specific remote for from about £5 upwards.

However these Varilight dimmers are smart - you can program them to do a bunch of things - depending on which model you have. It's not clear how to work that out (apart from testing it using its programming mode - see below), but all of them can be programmed to work with any remote control you have - e.g your TV remote. Just choose a spare button that you don't use and you can get the varilight to use it to turn the thing on and off! As mentioned here:

1. Tap switch 6 times - takes it in to 'learning mode' (After the 6 taps the light will go and off once more to indicate it's in learning mode).
2. Point your choose remote at it whilst pressing (for 2 secs or more) that your chosen button at it - the lights will go on and off.
3. Point the remote at the it again whist pressing the button and the lights should go on and off
4. You're done - it should work as your new remote control!

Dynamic library dependencies - direct or not?

So you're looking at some (Linux) binary and wondering what libraries it uses - You can use ldd to list all the dependencies:
ldd /path/to/your/app
However this shows direct and indirect (i.e. those needed by other libraries) dependencies, so you can tell what are just the direct dependencies by using readelf:
readelf -d /path/to/your/app
The direct dependencies are the libraries listed as NEEDED.

ssh key verification failed: how to check your fingerprints

So you ssh to a usual machine and get:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
3f:d6:e7:72:9a:ab:4e:e1:21:91:3a:88:6b:78:83:ce.
Please contact your system administrator.
Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message.
Offending key in /Users/username/.ssh/known_hosts:73
RSA host key for localhost has changed and you have requested strict checking.
Host key verification failed.

It's worrying.... Has someone hacked my machine (again!?). Or am I being paranoid for the 13th time this week?
This error is due to a mismatch between the RSA key that you already have stored on your machine in the /Users/username/.ssh/known_hosts file, and the one that ssh has just obtained over the network on this login attempt. Note: newer versions of ssh now store hashes of hostnames (see: ssh-keygen -H) in the known_hosts file to maintain privacy. Either the ssh server key has been changed legitimately (by you or some admin) or it's been hacked. It's also possible that someone on has set up a machine on the same IP address as the server you're trying to contact then you'll find you can't login - in which case you (or some admin) needs to track down the rogue machine.
To check the key is correct login to the machine in question - preferably on the console, but if you're connecting via ssh then you'll have to ignore the warnings above. Then you can directly print your server's key's fingerprint. There are a few types of keys: RSA, DSA, ECDSA (for SSHv2), and RSA for SSHv1. If your on a 'standard' Linux box then it's probably at: /etc/ssh/ssh_host_rsa_key.pub (or for DSA /etc/ssh/ssh_host_dsa_key.pub). If you're on a Mac OSX it is in: /etc/ssh_host_rsa_key.pub (or /etc/ssh_host_key.pub or /etc/ssh_host_dsa_key.pub). e.g. So on a Mac OSX box try:
% ssh-keygen -l -f /etc/ssh_host_rsa_key.pub
2048 3f:d6:e7:72:9a:ab:4e:e1:21:91:3a:88:6b:78:83:ce. /etc/ssh_host_key.pub
The key fingerprint (of the corresponding key type - in this case RSA) should match the one shown above. If these don't match then something fishy is going on....
Also just for info you can list all the fingerprints of all your stored host keys
% ssh-keygen -l -f .ssh/known_hosts
Instead you can just compare the public keys stored on your client in ~/.ssh/known_hosts with the keys on the server in /etc/ssh/ssh_host_*.pub

It is also possible that if you've upgraded your version of ssh (or altered your ssh-agent setup), and your machine has previously stored an RSA key in your ~/.ssh/known_hosts file but it is now getting an ECDSA key from the server which obviously won't match but may still be a valid key for that machine. It seems that ssh could work out this problem for itself without any lack of security but currently can lead to such warnings.

[22jan16: Updated to simplify and include ECDSA keys]

Getting ssh-agent going on Mac OSX

It seems irritating that OSX doesn't have an easy way to get ssh-agent running for a login session. However it can be done using launchd and a bit of scripting.

Before you start you'll need to have an /Users/username/.ssh directory (where username is your username) - or alter the scripts appropriately below. Create file /Users/username/Library/LaunchAgents/ssh-agent.plist containing:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.ssh.ssh-agent</string>
<key>OnDemand</key>
<false/>
<key>Program</key>
<string>/Users/username/.ssh/ssh-agent.sh</string>
<key>RunAtLoad </key>
<true/>
<key>ServiceDescription</key>
<string>Launch ssh-agent</string>
</dict></plist>

Then create a file /Users/username/.ssh/ssh-agent.sh containing:
#!/bin/sh
rm /Users/username/.ssh/ssh-agent.pipe
exec /usr/bin/ssh-agent -a /Users/username/.ssh/ssh-agent.pipe -d

Note: ssh-agent has to be started using -d option as launchd doesn't like processes to fork off into 'daemons'...probably why a few people don't like it.

Make the script executable:
$ chmod +x /Users/username/.ssh/ssh-agent.sh

Then ssh-agent will get started next time you login by launchd, or you can start it immediately by running:
$ launchctl start com.ssh.ssh-agent

Now you need to set the following environment variable (you can use RCEnvironment to set ~/.MacOSX/environment.plist) - probably easiest to add the following line to your /Users/username/.profile:
export SSH_AUTH_SOCK=/Users/username/.ssh/ssh-agent.pipe

You can then add your keys (assuming you've set 'em up using ssh-keygen or whatever) to the agent using:
$ ssh-add

Private searching

You don't want all your searching habits tracked then try scroogle (was black box but they evaporated) search, or if you're using Firefox check these search extensions.

Can't compile code using g2c.h (libg2c) on gcc4

I ran into this in trying to compile nettimer. If you're seeing compile (when using gcc-4.1) errors like:
/usr/include/g2c.h:21: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘integer’
Then, as suggested here, just add the missing typedefs to your code (then it _should_ work in gcc4.1):

// Typedefs to keep g2c.h happy
typedef int __g77_integer;
typedef unsigned int __g77_uinteger;
typedef long int __g77_longint;
typedef unsigned long int __g77_ulongint;

#include <g2c.h>

The alternative is just to use gcc-3.4 which apparently 'just works'.

What happened to my nvidia driver and where did it come from anyway?

Which package does nvidia.ko come from on debian Ubuntu (7.04) - as no package claims ownership when running dkpg -L . How to I regenerate/recreate nvidia.ko ?? I get errors in dmesg: nvidia.ko not found

It is generated by the lrm subsystem - linux-restricted-modules-2.* (Note: the module creation is controlled at bootup by /etc/default/linux-restricted-modules-common - make sure you haven't messed that filei - the modules created by /sbin/lrm-manager into a ramfs and mounted onto /lib/modules/2.6.XX-XX-generic/volatile) - why doesn't dpkg know??? (I guess since they're dynamic dpkg would need some more dynamic DB of such files...)

The nvidia.ko, nvidia_new.ko, nvidia_legacy.ko are loaded by the shell script /sbin/lrm-video (called from /etc/modprobe.d/lrm-video) based on [dot]trigger files in /lib/linux-restricted-modules/ e.g. .nvidia_new_installed

How to enable syntax highlighting in vim on Ubuntu

Uncomment (i.e. remove " at line start) containing:
"syntax on

Using your favourite editor as root e.g:
sudo vi /etc/vim/vimrc

Where are all these 'random' shares coming from in my Windows explorer under My Network Places ???

They are automatically culled from your network neighbourhood by the 'netcrawl' functionality of explorer - see: M$ KB, though the article isn't quite correct on reg path it is actually on WindowsXP: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\WorkgroupCrawler\Shares. Also intriguingly enough Explorer stashes all previously encountered machines at: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\ComputerDescriptions

openssh sshd replies : "Permission denied, please try again.", after attempting password login.

Make sure "PasswordAuthentication yes" is set in your sshd config file. Does your machine use PAM? (then check PAM setup). Your openssh may not be compiled to support PAM in which case does your machine use MD5 hashed passwords? (Hint: look in /etc/passwd or /etc/shadow and see if the password hashes are rather long and begin something like"$1$i..."). In that case try recompiling openssh with MD5 support (this is also good for standard linux installs): ./configure --prefix=/usr --sysconfdir=/etc/ssh --enable-ipv6 --with-md5-passwords . Thanks to SSH FAQ