Use sudo if you are not a root user.

On Linux operating systems, the sudo command(stands for "superuser do") is used to run commands with the root user's privileges.

This is done by entering sudo at the beginning of each line of commands. It prompts you for your personal password and confirms your request to execute a command by checking a file, called sudoers, which the system administrator configures. Using the sudoers file, system administrators can give certain users or groups access to some or all commands without those users having to know the root password. It also logs all commands and arguments so there is a record of who used it for what, and when.

Alternatively, one may become root (system administrator) by logging in as "root" or by using the su command. But root's password is required for becoming a root user :)