How to manage file or folder permissions between two user accounts on Linux

There are two users: the user jenkins and the user nginx (both are actually the service accounts).

First, the user jenkins creates the directory frontend in the /usr/share/nginx/html folder. Then it downloads some html files saving them in this folder.

Then the user nginx tries to open one of the html files and gets the Permission denied error.

To fix this issue, I first checked which groups the users belong to with: groups jenkins and it returns: jenkins : jenkins

Then I checked what group the user nginx is assigned to. And it is nginx : nginx

I checked the permissions for the frontend folder jenkins created as /usr/share/nginx/html/frontend and it it is automatically assigned the user jenkins and the group jenkins. Via changing the permissions for this folder with chown command I found that in order for nginx user to be able to read these files the folder needs to be set with nginx:nginx ownership.

I have also tried to create a new group workers and then assign both jenkins and nginx users to it with

sudo groupadd workers 
sudo usermod -aG workers jenkins
sudo usermod -aG workers nginx

But unfortunately, that didn’t fix the issue. jenkins user keeps creating the folders with the same ownership as before jenkins:jenkins.

Is there a way to make both users have a full access on a folder created by one of them? What should I do?

P.S.

Below is some additional info. The frontend folder is created by jenkins user in /usr/share/nginx/html/. Here are some details:

sudo namei -om /usr/share/nginx/html/

    f: /usr/share/nginx/html/
     dr-xr-xr-x root  root    /
     drwxr-xr-x root  root    usr
     drwxr-xr-x root  root    share
     drwxr-xr-x nginx jenkins nginx
     drwxrwxrwx nginx nginx   html

Then, after the frontend folder is created I run

sudo namei -om /usr/share/nginx/html/

to check its ownership and it is:

    f: /usr/share/nginx/html/frontend
     dr-xr-xr-x root    root    /
     drwxr-xr-x root    root    usr
     drwxr-xr-x root    root    share
     drwxr-xr-x nginx   jenkins nginx
     drwxrwxrwx nginx   nginx   html
     drwxr-xr-x jenkins jenkins frontend

Answer : Edited later:

Below is a breakdown of the steps needed to make a single folder created by one user accessible by another.

1. Create a new user group and assign both user to it:

sudo groupadd newgroup
sudo usermod -aG jenkins
sudo usermod -aG nginx

2. Now, after jenkins user creates a folder with the default jenkins:jenkins ownership, make jenkins user change the folder’s ownership setting it with jenkins:newgroup (note that jenkins won’t be able to set the folder’s group ownership to newgroup unless it is a member of newgroup):

chown -R jenkins:newgroup /path/to/folder/created/by/jenkins/

3. Make jenkin user to assign read-write permissions to the owner user (jenkins) and owner group(newgroup) by running:

chmod -R 775 /path/to/folder/created/by/jenkins/

Answer

can you try using the “chgrp” command after creating the directory?

chgrp groupname directoryname

After that, do a chmod to allow full access to the group.

chmod 775 directoryname

That will allow both to access.