SSH Keys and Windows, basic no passphrase

For most people GIT access is controlled via username and password, this is fine when working only a small project, when rarely doing push and pull from your remote repos online. However the next step is to use an SSH key.

This mean that you share some information between your PC and the remote server, these are called keys, for the uninitiated. Using the Git for Windows installer and OpenSSH you can generate and configure an SSH key for the connection.

Disclaimer - This is not the most secure method but is meant to be a stepping stone to passphrase based SSH with an agent.

To create an SSHKey look to use the ssh-keygen application that comes with GIT for windows.

The SSH-keygen application is normally stored in the C:\Program Files\Git\usr\bin\ and a key can be generated with the following command

"ssh-keygen" -t rsa -f bitbucket_rsa -N ""

Details:
-t type RSA
-f filename butbucket_rsa
-N passphrase

The command above creates a key pair in the current directory called bitbucket_rsa and bitbucket_rsa .pub with no passphrase. You will need to copy the bibucket_ras to the ~.ssh folder in your user directory.

To make the PC use the private key (bitbucket_rsa) when making the connection, you can use the config file in the ~/.ssh directory. This file is formatted in the following way.

host bitbucket.blah.com
IdentityFile ~/.ssh/bitbucket_rsa

Details
host then the URL of the server that you are making the connection to.
Identify file this is the location of the private key file.

To add a ppublic key into your bitbucket account you need to do the following:

• Sign in to bitbucket
• click the top right hand profile button
• click the manage account button
• click SSH keys
• click on the add key button
• copy and paste the contents of the bitbucket_rsa.pub into the text box and then click add key.

Your key is now on the server.

When you make the first connection over command line to the server, you will be asked if you accept the host key the server and a finger print will be shown much like below:

[bitbucket.com]:3456,[0.0.0.123]:9090 ssh-rsa RRRB3NzaC1yc2EAAAADAQABAAABAQCch1FyAnxrvKPw7AkhVyfR9FOJNVzIAUfgxlhHDR7rafYgmJkSwUCZtsYKRv6wNUEeRHh5EU/yYr/2zn0+5l2A/AG6X95SwrBBSzpeelFo2hoIjIZmnHv93k5VK0OXfpAfKqBRDMY5s1tVcdyKa6qCirHydyYbViM3Ob3mBhrhY/w87jXZqaMLQlNUbMfH6iGdaVBNeqgqSPeclgHge7kwSoIukMY0pqiQAinS0bb3aPzl4dwNCJBrghV1eYKGHL7/ESX+Mj8PrsJDzWv1IxG6Ey5jjcY+zw/386sKY2QbmB55m91lg50LfEZP/1OorbLBxDqThAW5maU7J27knGaR

Once verified this will be contained in a knownhosts file in the .ssh directory, the same location as the config file and the private key.

Now you should have a very simple SSH connection available.

Restart Windows machine remotely.

Let's face it sometimes you have to restart a machine.

But it's a VM, or you remote into the machine so you don't have access to the machine itself.

You need a way to restart a machine remotely and easily without having to remote in each time you want to do it.

You need the shutdown command that's in the command prompt. It takes the following arguments.

Parameter	Function
-s	Shuts down the computer.
-r	Reboots the computer.
-f	Force-close all running applications.
-m \\Computer	Specifies a specific computer on the network that you want to shut down or reboot. Absent this parameter, the command affects only the local PC on which it is run.
-t xx	Sets a delay (xx seconds) before the specified operation commences.
-c "message"	Add your own text inside the quotations to provide remote users with a message about why and when their PC will shut down or reboot.
/a	Aborts a shutdown or restart if used during the (-t) delay period.
/h	Hibernates the computer.
/?	Displays the full help document with all commands.

Now imagine that you need to restart a bamboo agent cluster as you updated the server and it requires a restart of the agents.

No problem as you can whip up a bat file to go through the cluster restarting the agents. 

shutdown -f-r -m \\computer1

shutdown -f -r -m \\computer2

Now you have a simple script to restart a bank of computers without any trouble, no logging in or remotely accessing the machines.

Creating PyVisa Wheel install on Windows

So I have some legacy software that requires PyVisa 1.3 and I'm building wheels for all the packages that require this as this is the new standard for python packaging.

I was having issues creating the wheel file or even installing from the tar file from PyPi until I came across this bug report and it worked a treat.

To sum up all the actions that I needed to do.

1. Get the Tar file.
2. Extract the source.
3. make the following changes

setup.cfg:
-prefix = /usr 

In 'setup.py' home_dir can be derived in a platform independent fashion:
setup.py:
- home_dir = os.environ['HOME']
+ home_dir = os.path.expanduser('~')

4. Navigate to the root of the source and make the wheel file

python setup.py bdist_wheel

Viola you have a windows wheel file that can be installed fast and effective to all virtual environments.

The newer versions are much easier to package into wheel files. I will be sure to post up about other packages that I have any issues with and the solutions to them as well.

Reserved Filenames on Windows

So today I was working on a full Atlassian product suite, you know Stash, Bamboo, JIRA. And we had a well known code base (the Linux kernel itself) that we are compiling on our Linux build agent.

However one of the development platforms is Window 7 (yes Windows 7 doesn't develop the Linux kernel but this is a test of the product suite and not windows 7 ability to compile the Linux kernel). So I'm cloning the Linux Kernel from Stash to Window 7 and it fails half way through and I'm thinking "Oh no Stash and Git must be configured incorrectly."

Once inspecting the git errors however it was complaining of

fatal: git rm: 'drivers/gpu/drm/nouveau/nvkm/subdev/i2c/aux.c': Permission denied

Obviously this had me trying again and then trying to create a file called aux.c on the desktop.

Queue a most random error from a file creation I have seen

The error was "specific device name is invalid" when creating the file aux.c on the desktop. Now as you can tell this got my interest and so off to google and windows and aux.c.

This lead me to an interesting little knowledge base article

https://support.microsoft.com/en-gb/kb/74496

where it details that some filenames on windows are reserved for certain things.

  Name    Function
   ----    --------
   CON     Keyboard and display
   PRN     System list device, usually a parallel port
   AUX     Auxiliary device, usually a serial port
   CLOCK$  System real-time clock
   NUL     Bit-bucket device
   A:-Z:   Drive letters
   COM1    First serial communications port
   LPT1    First parallel printer port
   LPT2    Second parallel printer port
   LPT3    Third parallel printer port
   COM2    Second serial communications port
   COM3    Third serial communications port
   COM4    Fourth serial communications port

Has anyone ever come across this before, it such an oddity of Windows to do this.....