Which command allows a user to switch to another user in Linux?

The command that allows a user to switch to another user in Linux is "su." This command stands for "substitute user" or "switch user." When executed, it enables the user to temporarily assume the identity of another user, provided they know the password of that user. This is particularly useful for system administration tasks, as it allows users to execute commands with the permissions of the target user without needing to log out and log back in.

In contrast, the other options serve different functions: "ps" is used to display information about currently running processes; "ifconfig" is a command used to configure network interfaces; and "ll" typically lists files in a directory in long format, but it is not a standard command on all Linux distributions as it is an alias for "ls -l". Each of these commands plays an important role in system management but does not facilitate user switching like "su" does.