Powershell on Cumulus Linux


Userlevel 2
Microsoft recently released Powershell for Linux. Since Cumulus Linux is Linux, you can install Powershell directly on your Cumulus Linux switch.

Quick Links:
Microsoft Powershell for Linux: https://github.com/PowerShell/PowerShell
Ansible Playbook to install Powershell on Cumulus Linux: https://github.com/plumbis/demos/blob/master/install_powershell.yml
Example Powershell script: https://github.com/plumbis/demos/blob/master/powershell_interfaces.ps1

This was my first experience with Powershell, but the power of Powershell as a Cumulus Linux scripting language is clear. For those coming from a Windows admin background this is a big deal.

First, to install Powershell on Cumulus Linux:
  1. Add Debian Sid and Debian Jessie Apt repos to /etc/apt/sources.list
    deb http://ftp.us.debian.org/debian/ sid main contrib non-free 
    deb http://ftp.us.debian.org/debian/ jessie main contrib non-free
  2. Apt pin libstdc++ to Debian Sid. This is required for the prerequisites for Powershell. To do this, create the file /etc/apt/preferences.d/30_powershell_sid and put the following in the file
    Package: libstdc++6 
    Pin: release n=sid 
    Pin-Priority: 999
  3. Refresh the Apt cache apt-get update
  4. Install libunwind8 and libicu55 Powershell prerequisites
    apt-get install libunwind8 libicu55 
    
  5. Download Powershell .deb for Ubuntu 16.04 from the Powershell Github page
  6. Install Powershell using dpgk -i
  7. Finally, modify the virtual memory limit for the system. This can be done in a temporary (for the length of your SSH session) or permanent manner. Temporary increase is good for one-time Powershell usage or testing. Permanent increase could create issues if a process is out of control. Change with caution. Temporarily Increase Virtual Memory
    ulimit -v unlimited
    Permanently Increase Virtual Memory Edit /etc/security/limits.d/99-cumulus.conf and replace
    1:  soft  as        1048576
    with
    1:  soft  as        unlimited
    This change will take effect on the next user login. Failure to change the virtual memory limits will result in the following error:
    vagrant@spine1:~$ powershell 
    cannot allocate memory for thread-local data: ABORT
  8. Now you can run Powershell with the powershell command!
    vagrant@spine1:~$ powershell 
    PowerShell 
    Copyright (C) 2016 Microsoft Corporation. All rights reserved. 
     
    PS /home/vagrant>
I also created an Ansible playbook that will execute the same steps. This can be found on github.

With Powershell installed we can start automating. I wanted to tackle something simple, since I'm still new to Powershell. A common need for customers is to bring up all of the interfaces on their switch after applying a license. To do this you must add an auto and iface line for every port in the interfaces file. Sounds like a perfect task to automate.

I went about writing a Powershell script to look at the output of /proc/net/dev to find a list of all swp interfaces, and then put populate /etc/network/interfaces with "auto swp" and "iface swp"

My script can be found on my personal github. A few highlights:
First pulling the output of /proc/net/dev and placing it in the variable $proc_dev
$proc_dev = (get-content /proc/net/dev)

Next, looping through the output, splitting the line based on the ":" delimiter and then grabbing only the lines with "swp" in them.
foreach($line in $proc_dev){ 
$temp = $line.split("\:")[0].Trim()
if($temp.contains("swp")){
$iface_array += $temp
}
}
Finally, writing the output to the /etc/network/interfaces file
Write-Output $output_array | Out-File -encoding ASCII /etc/network/interfaces
This is a basic example of what Powershell can do, but beyond this example it highlights the power of an open platform like Cumulus Linux. When the Linux community releases a new tool like Powershell, you can utilize immediately without waiting for patches or updates from the vendor.

Happy Powershelling!

5 replies

Nice work Plumbis.
Hi, I am trying to install PowerShell on Cumulus Linux 3.3.2. Missing libicu55?
Userlevel 2
SHE wrote:

Hi, I am trying to install PowerShell on Cumulus Linux 3.3.2. Missing libicu55?

It looks like a package may have changed in the repo. Let me dig into it and see if I can get an answer for you.
Userlevel 2
SHE wrote:

Hi, I am trying to install PowerShell on Cumulus Linux 3.3.2. Missing libicu55?

SHE, please try again. It looks like we updated the packages in our repo with the 3.4 release and I was able to follow the Microsoft instructions and install Powershell on both 3.3.2 and 3.4.0. You will still need to adjust the memory limits as described in this KB
SHE wrote:

Hi, I am trying to install PowerShell on Cumulus Linux 3.3.2. Missing libicu55?

Now it's working! Thanks.

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