sudo allows users to run programs with the security privileges of another user (superuser or other users). Of the supported options, what’s difference between -s and -i?

Both options run an interactive shell if no command is specified:

1
2

$ sudo -s
$ sudo -i

The difference is that when using -i:

sudo attempts to change to that user’s home directory before running the shell. The command is run with an environment similar to the one a user would receive at log in. - man sudo

Let’s assume the current directory is at /:

1
2
3
4
5

$ sudo -s pwd
/
$ sudo -i pwd
/root

Changing directory is not attempted when using -s option.

sudo is commonly used to elevate the privilege to execute as the superuser, and usually done in place rather than in the superuser’s home directory, such as:

1

$ sudo -s chown $USER:$GROUP file

Therefore, when running as superuser, use -s:

1

$ sudo -s

When running as another user, use -i:

1

$ sudo -u foo -i

Commands:

1
2
3
4

$ curl -sSL https://get.docker.io/ubuntu/ | sudo sh
$ sudo usermod -a -G docker $USER
$ sudo service docker restart
$ logout

Explanation:

1. One line command installation
2. Add the user to the group docker
3. Restart the daemon
4. Make sure to logout and log back in, in order to sudoless Docker taking effect.