Which command should be used to verify the existence of a user in a Linux system?

The command used to verify the existence of a user in a Linux system is the "id" command. When executed with a username as an argument, it retrieves and displays information about the specified user, including the user's UID (User ID), GID (Group ID), and any supplementary groups to which the user belongs. If the user does not exist, the command will return an error message indicating that the user was not found.

This makes the "id" command a straightforward and effective way to confirm whether a user is present on the system, along with some of their attributes.

The other options serve different purposes. For instance, "checkuser" is not a standard command in most Linux distributions and may not even exist, which renders it ineffective for this purpose. The "usermod" command is used to modify user accounts rather than check for their existence; therefore, it does not fulfill the requirement of simply verifying if a user exists. "getent," while it can be used to query the user database and retrieve information about users, is typically used for more complex queries and requires familiarity with the databases defined in "/etc/nsswitch.conf." Thus, while "getent" could also be used to achieve this, the "id"