useful_ubuntu

Merge pdf files

Ghostscript is a package (available by default in Ubuntu) that enables you to view or print PostScript and PDF files to other formats, or to convert those files to other formats. To use Ghostscript to combine PDF files, type something like the following:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dAutoRotatePages=/None -sOutputFile=output.pdf  input_file1.pdf input_file2.pdf

Some explanation

gs         starts the Ghostscript program.
-dBATCH    once Ghostscript processes the PDF files, it should exit.
           If you don't include this option, Ghostscript will just keep running.
-dNOPAUSE  forces Ghostscript to process each page without pausing for user interaction.
-q         stops Ghostscript from displaying messages while it works
-sDEVICE=pdfwrite 
           tells Ghostscript to use its built-in PDF writer to process the files.
-sOutputFile=finished.pdf
           tells Ghostscript to save the combined PDF file with the specified name.
-dAutoRotatePages=/None
           Acrobat Distiller parameter AutoRotatePages controls the automatic orientation selection algorithm: For instance: -dAutoRotatePages=/None or /All or /PageByPage.

ref: https://askubuntu.com/a/257170/996807

Use python virtualenv with jupyter notebook

Create the python virtual environment, activate and install ipykernal

python3 -m venv ./venv_name
source ./venv_name/bin/activate
pip install ipykernal
python3 -m ipykernel install --user --name=venv_name

Image and videos

Convert images sequences to videos

ffmpeg -framerate 20 -i %06d.png -codec copy output.mp4

Convert videos to images

# extract every 1 second
ffmpeg -i video.MP4 -vf fps=1 %6d.png

Access ubuntu workstations in the local network

ssh <username>@<computer_name>.local