The error message is telling you that it can't access/save the file. Make sure the user you are running the commands has the proper permissions.
I wondered that too, I was using a user I specifically created for this task in order to not use the root user as I thought it was not a good practice to do. Especially since the instructions indicate a sudo user. Usually I can figure out permission issues, but for some reason I have not been able to solve this one. The installation does get further when using the root user, so there is definitely a permission issue.
The error I get now is related to the connection of the Redis database. I get a connection refused error when using the IP of the server.
The abort error shows the IP address and default port number so I have no idea how to connect the database.
Here's the latest console information ...firstname.lastname@example.org node_modules/connect-redis └── email@example.com (firstname.lastname@example.org) 25/4 19:08  - info: Populating database with default configs, if not already set... 25/4 19:08  - error: Error: Redis connection to myserverIP:6379 failed - connect ECONNREFUSED at RedisClient.flush_and_error (/mydomainpath/nodebb/node_modules/redis/index.js:142:13) at RedisClient.on_error (/mydomainpath/nodebb/node_modules/redis/index.js:180:10) at Socket.<anonymous> (/mydomainpath/nodebb/node_modules/redis/index.js:95:14) at Socket.EventEmitter.emit (events.js:95:17) at net.js:441:14 at process._tickCallback (node.js:415:13) 25/4 19:08  - warn: NodeBB Setup Aborted. Redis connection to myserverIP:6379 failed - connect ECONNREFUSED
Thanks ... Pops