I managed to follow all the steps to create EC2 instance and install R Server on it.
When I go to RStudio Server page to connect (which looks something like "ec2-[Public IP]-.eu-west-3.compute.amazonaws.com:8787"), I am asked a username and a password.
I figured out to set a username ("user1") this way:
$ sudo useradd user1
But then when I try this command to write the password:
echo user1:password | chpasswd
I receive this message: chpasswd: cannot lock /etc/passwd; try again later.
I looked at different solutions suggested here:
but I do not see a resolution to my problem.
I did not find either any passwd.lock, shadow.lock, group.lock, gshadow.lock files to remove.