Git: git clone – fatal: unable to fork and RSA key fingerprint

By | 10/23/2020

We have a Docker image with Git client installed.

The task is to automatically clone a repository when running a container from this image.

git clone – fatal: unable to fork

When running the git clone command in a container from this Docker image it fails with the “unable to fork” error:

[simterm]

/ # git clone [email protected]:projectname/backend-services.git
Cloning into 'backend-services'...
fatal: unable to fork

[/simterm]

The cause is that git uses SSH for authentication here ([email protected]), but we have no ssh client installed in the image:

[simterm]

/ # ssh
sh: ssh: not found

[/simterm]

Install it:

[simterm]

/ # apk update
/ # apk add openssh

[/simterm]

The authenticity of host ‘github.com’ can’t be established

Another issue when automating git clone – it’s asking to confirm the RSA key from the github.com host:

The authenticity of host ‘github.com (140.82.121.4)’ can’t be established.
RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
Are you sure you want to continue connecting (yes/no)?

To solve this – need to add its public key to the ~/.ssh/known_hosts file.

Use ssh-keyscan for this:

[simterm]

/ # ssh-keyscan github.com >> ~/.ssh/known_hosts                                                                                                                                                                                             
# github.com:22 SSH-2.0-babeld-1a846ed2                                                                                                                                                                                                      
# github.com:22 SSH-2.0-babeld-1a846ed2                                                                                                                                                                                                      
# github.com:22 SSH-2.0-babeld-1a846ed2

[/simterm]

And now clone the repository:

[simterm]

/ # git clone [email protected]:projectname/backend-services.git
...
remote: Total 5115 (delta 96), reused 169 (delta 56), pack-reused 4871
Receiving objects: 100% (5115/5115), 846.55 KiB | 3.00 MiB/s, done.
Resolving deltas: 100% (2826/2826), done.

[/simterm]

Done.