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Changing Identities
At various times, we may find it necessary to take on the identity of another user. Often we want to gain superuser privileges to carry out some administrative task, but it is also possible to “become” another regular user for such things as testing an account. There are three ways to take on an alternate identity:
1. Log out and log back in as the alternate user.
2. Use the su command.
3. Use the sudo command.
We will skip the first technique since we know how to do it and it lacks the convenience of the other two. From within our own shell session, the su command allows you to as- sume the identity of another user, and either start a new shell session with that user's IDs, or to issue a single command as that user. The sudo command allows an administrator to set up a configuration file called /etc/sudoers, and define specific commands that particular users are permitted to execute under an assumed identity. The choice of which command to use is largely determined by which Linux distribution you use. Your distri- bution probably includes both commands, but its configuration will favor either one or the other. We'll start with su.