To install/update on linux use this command and avoid distribution specific packages (to get the latest version) as per https://calibre-ebook.com/download_linux

sudo -v && wget -nv -O- https://raw.githubusercontent.com/kovidgoyal/calibre/master/setup/linux-installer.py | sudo python -c "import sys; main=lambda:sys.stderr.write('Download failed\n'); exec(sys.stdin.read()); main()"

Configuration can be copied from a previous windows installation. Essential files on the linux system are in $HOME/.config/calibre and they are customize.py, global.py, gui.py, tweaks.py and possibly the .json files. Ensure to edit the files and change all path references.

Copied plugin files don't appear to work, but need to be installed separately. This may be due to different versions or due to different install-id in the config file.

Note:

When mounting cifs share and using calibre database on that share, use the 'nobrl' mount option to avoid locking issues and incorrect error messages.

see https://bugs.launchpad.net/calibre/+bug/1760535

Source: https://medium.com/@angeldan1989/a-complete-guide-to-convert-kobo-to-epub-pdf-kindle-d8523197d927

Step 1. Download Kobo books to Computer/Kobo eReader first.
Downloading Kobo titles onto Kobo eReader or the Kobo desktop will download eBooks in .kepub format (and kepub drm), But downloading Kobo books from Kobo's official site (“My Books”), the file will be .acsm files (in fact they are .epub or .pdf, adobe adept drm adopted).

Note: .acsm files require the use of Adobe Digital Editions (Adobe ID) to deDRM.

Step 2: Convert Kobo (KEPUB) to ePub/PDF/Mobi and Remove DRM.

Tools we will need: Calibre; obok_plugin v6.5.4 (https://www.epubor.com/download/obok_plugin.zip).
Run Calibre, and then add the newly downloaded obok_plugin.zip into Calibre.

Preferences → Plugins → Load plugin from file

Once the plugin added well, restart Calibre, you will find it from the top menu bar.

Click on the plugin, it will show all your downloaded KEPUB books. Choose books and select “OK”.

Soon the kobo kepub drm removing begin. I must say that this plugin is so powerful that all kobo books drm will be finished within several seconds. From the right side area you will found that the drm free kobo books will be EPUB (not .kepub).

By this method we can extract kobo kepub to common ePub format.

Step 2 (optional). Remove Kobo DRM from Kobo ACSM and convert formats.

What if I downloaded the kobo books from kobo library online (.acsm)? In this situation firstly use Adobe Digital Editions (Adobe ID, the same email address as your kobo account please) to download the kobo acsm as ePub/PDF please.

Then, download Calibre DeDRM_plugin.zip (v 6.6.3) and add it into Calibre please. More info read my previous blog Calibre DRM Removal Plugins 2019 please. https://medium.com/@angeldan1989/calibre-drm-removal-plugins-2019-remove-ebook-drm-with-calibre-4ec9c07cae80

Restart Calibre, choose the kobo books you want to convert. By default, once books added into the library, the drm will be removed soon, then you can continue to convert the formats by “Convert books” → Output format selecting.

But if you failed (Calibre failed to find out the corrent Adobe adept key file), find the newly added dedrm plugin → Customize plugin → Adobe Digital Editions ebooks.

DeDRM → Customize plugin → Adobe Digital Editions ebooks

Soon the plugin will list all the key files. This means, if you used different Adobe ID to sync your books, there will be different key files.

So make sure use the same email address as your kobo account to authorize the Adobe ID please, this is very important. And just because of this point, someone will get stuck with this method. Use correct Adobe ID and make sure you can open your kobo acsm with ADE please!

The bottom line: Tips&More.

1. Kobo books will be adopted in different drm scheme and format. In a word, if books are downloaded via Kobo its desktop app or eReader, Kobo unique drm and format — KEPUB; If books are downloaded via Adobe Digital Editions, they are bundled with Adobe DRM — ACSM.
2. Different DRM scheme, different Calibre plugin to be installed. But for 100% success to remove drm from kobo books, I highly recommend you use Kobo desktop app/eReader to download kobo books, not the ADE! Trust me it’s an easier method, saves your time much.
3. Where are my kobo books stored on my Mac or Win 10 computer? By default they are actually stored in kepub format in …\Kobo\Kobo Desktop Edition\kepub. If you download books via ADE, they are in … /My Documents/My Digital Editions.
4. Why I need to convert Kobo books to ePub or PDF or Kindle mobi? You own your books, your own your devices, yes there is no need to convert the formats. Here I write down this blog is just for those people who want to back up/share their kobo books (for personal use), or who want to read purchased kobo eBooks on Kindle Paperwhite, or who want to read kobo books on non-Kobo apps!
5. Calibre and the plugins are free. But if you think it’s not so easy to use especially when loading plugin files to remove the drm, or if you met problems but didn’t find the answer, here is a good alternative — Epubor Ultimate. It’s paid software, but it’s 24 hour online customer service. What’s better, it automatically detects all the kobo books (both kepub and acsm epub), this saves our time to search the files location, right?