Python introspection blog post

 A great blog post about how to use python modules to inspect python code itself can be found here

Veiryfing ssh fingerprints of a system

When trying to connect to a system via ssh for the first time you will get a message that you need to trust the ssh fingerprint of that system.

How do you know if the fingerprint displayed is the correct one, or if there is a man in the middle attack going on?

If you have another terminal open on the system you have you can go to /etc/ssh and execute the following:

for file in *sa_key.pub
do   ssh-keygen -lf $file
done

This will diplay the ssh fingerprints valid for this system so you can double check them.

Enabling multiple displays with Thinkpad P52

When switching to power save mode nvidia disables the graphics card multiple display support.

It does not enable it back when switching to performance mode. This was done by creating a file in /lib/modprobe.d/nvidia-kms.conf and setting modeset to 1.

We can revert this change by changing the modeset to 0 or commenting this line. After rebooting, the external display works again.

Separating filename from extension in bash

If we want to separate filename from extension in bash this is a neat and useful trick:

filename=$(basename -- "$fullfile")
extension="${filename##*.}"
filename="${filename%.*}"

Prioritization of network interfaces

If we have more than one network interfaces and want to prioritize routing via one of them we can do the following:

Check the priorities in the routing table:

/home/nickapos [nickapos@nickapos-ThinkPad-P52] [8:44]
> ip route                    
default via 192.168.17.1 dev enp0s31f6 proto dhcp metric 100
default via 192.168.1.254 dev wlp0s20f3 proto dhcp metric 600

Here we can see that we have two interfaces with different metric values enp0s31f6 has higher priority than wlp0s20f3, if we want to swap them we need to install ifmetric with

sudo apt install ifmetric 

and do:

sudo ifmetric wlp0s20f3 99

After this if we check the routing table:

/home/nickapos [nickapos@nickapos-ThinkPad-P52] [8:45]
> ip route                 
default via 192.168.1.254 dev wlp0s20f3 proto dhcp metric 99
default via 192.168.17.1 dev enp0s31f6 proto dhcp metric 100

we can see that wlp0s20f3 has higher priority so routing will happen by default through it. Only packages that can not be served by it will be routed via enp0s31f6,

Python patterns and antipatterns

Discovered a nice online python book about patterns and antipatterns here https://docs.quantifiedcode.com/python-anti-patterns/

Parsing and validating YAML

For anyone who is looking for ways to validate YAML files, there are multiple modules out there for python, ruby and perl.

If using pip then you can install yamllint program:

 pip install yamllint

and then do 

yamllint blah.yml

in Ruby you could do:

ruby -ryaml -e "p YAML.load(STDIN.read)"< data.yaml