Amazon Linux add user to group

Question

I am using Amazon Linux AMI image doing development. And I want to add the default user 'ec2-user' into group 'docker' like below:

sudo groupadd docker
sudo gpasswd -a ec2-user docker

When I logged in as user ec2-user, and run groups ec2-user, it shows:

ec2-user : ec2-user wheel docker

And this seems to indicate the 'ec2-user' was added to group 'docker'. However, if I run groups command without any parameter, which should be the same as groups ec2-user because I logged in as ec2-user, it shows:

ec2-user wheel

And it tells me ec2-user is not in the group 'docker' yet (actually it was not added to this group because permission error was reported when I tried to access some file belongs to group 'docker').

And this does not happen if I try to add the 'ec2-user' into group in this way:

sudo gpasswd -a ${USER} docker

And I found I can add other user name like 'harry' into group like below without any problem:

sudo gpasswd -a harry docker

My question is what is the cause for this behavior? It seems there is something wrong with this particular user name 'ec2-user' when adding it to a group but I have no idea why this happens. Any help is appreciated. Thanks.

Solution

The current shell was initialized before you added yourself to the group, so it cannot reflect a later change to your group memberships. You can

exec sg docker

to replace the current shell with a new one which is explicitly switched to the group you added yourself to, or simply log out and back in.

Comments

[Panther]

You have to log out and back in or start a new log-in shell for changes to your group membership to become effective.

[nybon]

@bodhi.zazen but it is not the case for other users I created such as 'harry' in the example. Once I created use 'harry' and added it into a group using gpasswd command, I can see it added to group immediately without logging out.

[David A. Gray]

Taking into account the comment, this answer is correct, and deserves to be marked as accepted.