How to enable PDF to CBR in docker?

[op4lat]

I am excited to see that the conversion of CBR has been added, but how do I enable it? The release notes say PDF to CBR (requires you to manually install rar due to license requirements) but I couldn't find instructions of how to do so. I entered the container command line and tried:

apk update
apk add --no-cache unrar

but I got

ERROR: unable to select packages:
  unrar (no such package):
    required by: world[unrar]

or I am supposed to do:

# Update the package list
apk update

# Install necessary build tools
apk add --no-cache --virtual build-dependencies gcc musl-dev

# Download the source code for both rar and unrar
wget https://www.rarlab.com/rar/rarlinux-x64-711.tar.gz

# Extract the archive
tar xzvf rarlinux-x64-711.tar.gz -C /tmp

# Copy the binaries to a system directory
cp /tmp/rar/rar /usr/local/bin/
cp /tmp/rar/unrar /usr/local/bin/

# Clean up
rm -rf /tmp/rar rarlinux-x64-711.tar.gz
apk del build-dependencies

[balazs-szucs]

Hi @op4lat,

Yes, this is very fair question. Generally unrar is for CBR to PDF, the "plain" rar libary is for PDF to CBR.

Tbh, I haven't tested in docker, but you are on the right track that you are going to need to build it, and there is not really an actual alpine package for it. AFAIK arm + alpine is no-go for rar, on X86 you should be able to build it (at least I believe so). I'll test my docker instance see what's up, and include better guide. Locally, if you really need it you can easily get it work by installing rar via your distro's repo. E.g., sudo apt install rar etc...

Sadly, there is real possibility that will need to clone the repo and build the docker container yourself and modify Dockerfile to make this work.

See here:
https://stackoverflow.com/questions/64715884/how-do-i-install-rar-in-a-alpine-based-container

There is not much we can do, the license really prohibits us from actually including any rar binary with the "official" image. Also please note: if you want "good" compatibility prefer CBZ over CBR. Currently, PDF to CBR makes RAR5.

[op4lat]

Thanks for the clarification. I changed the title to specify that this is a docker question.

[op4lat]

Welp. I tried the downloading the binary from rarlab version and it worked

spdf  | 17:04:17.734 [qtp2047734670-73] INFO  s.s.common.util.ProcessExecutor - Running command: rar a -m5 -ep1 output.cbr page_001.png
spdf  | 17:04:17.739 [Thread-28] INFO  s.s.common.util.ProcessExecutor - 
spdf  | 17:04:17.739 [Thread-28] INFO  s.s.common.util.ProcessExecutor - RAR 7.11   Copyright (c) 1993-2025 Alexander Roshal   20 Mar 2025
spdf  | 17:04:17.739 [Thread-28] INFO  s.s.common.util.ProcessExecutor - Trial version             Type 'rar -?' for help
spdf  | 17:04:17.739 [Thread-28] INFO  s.s.common.util.ProcessExecutor - 
spdf  | 17:04:17.740 [Thread-28] INFO  s.s.common.util.ProcessExecutor - Evaluation copy. Please register.
spdf  | 17:04:17.740 [Thread-28] INFO  s.s.common.util.ProcessExecutor - 
spdf  | 17:04:17.740 [Thread-28] INFO  s.s.common.util.ProcessExecutor - Creating archive output.cbr
spdf  | 17:04:17.746 [Thread-28] INFO  s.s.common.util.ProcessExecutor - 
spdf  | 17:04:17.753 [Thread-28] INFO  s.s.common.util.ProcessExecutor - Adding    page_001.png                                                OK 
spdf  | 17:04:17.753 [Thread-28] INFO  s.s.common.util.ProcessExecutor - Done

Not sure if apk add --no-cache --virtual build-dependencies gcc musl-dev is actually needed since I didn't compile anything

[balazs-szucs]

Nice!

Can confirm! TLDR:

1. Download rar from rarlabs
2. Move it to PATH and make it executable:

sudo mv /path/to/rar /usr/local/bin/rar
sudo chmod +x /usr/local/bin/rar

3. Add rar path to the docker container via env variable e.g.,

  stirling-pdf:
    image: ghcr.io/stirling-tools/stirling-pdf:alpha
    container_name: stirling-pdf
    environment:
      - PUID=1001
      - PGID=1001
      - TZ=Europe/Vienna
      - DOCKER_ENABLE_SECURITY=false
      - LANGS=en_GB
      - pull=always
    volumes:
      - ./docker/stirling/config:/usr/share/tessdata
      - ./docker/stirling/extraConfigs:/configs
      - ./docker/stirling/customFiles:/customFiles
      - ./docker/stirling/logs:/logs
      - ./docker/stirling/pipeline:/pipeline
      - /usr/local/bin/rar:/usr/local/bin/rar:ro # ADD THIS!

[balazs-szucs]

I'll make a PR for this, probably nice to have somewhere in the docs. Many thanks for the suggestion/raised ticket @op4lat!

[balazs-szucs]

Yeah, on my ARM VPS, it does not seem to work sadly. On X86 probably works just fine.

[balazs-szucs]

In the meantime the final draft of the new docs is available at: https://github.com/balazs-szucs/Stirling-PDF/blob/rar-guide/HowToSetupRAR.md

[op4lat]

Nice!

RAR is shareware. While it is free to use for personal, non-commercial purposes, business or commercial use may require purchasing a license. Please review the official RAR license terms on the RARLAB website for complete details.

While it is free to use for personal, non-commercial purposes, business or commercial use may require purchasing a license.

Is that from any of the Rarlab files? me grammar no good, but I'm sure those commas are confusing 👼

[balazs-szucs]

The "While" is meant to highlight the contrast between the two different use-cases, personal, non-commercial purposes vs business or commercial

Basically:

1. part: While it is free to use for personal, non-commercial purposes
2. part: business or commercial use may require purchasing a license.

See here for explanation: https://learnenglish.britishcouncil.org/grammar/c1-grammar/contrasting-ideas

[op4lat]

I see. Thank you for the thoughtful explanation!

[balazs-szucs]

Hi, in the meantime PR was raised for this on the docs repo see here: Stirling-Tools/Stirling-Tools.github.io#90

So, I am going go close this :)

Thanks for the ticket and research once again