The yum (apt-get or apt in Ubuntu) command is used to install new packages and to update/upgrade the operating system, it requires administrative access, so it must be used with sudo.
yum [OPTIONS] [COMMAND]
apt-get [OPTIONS] [COMMAND] (Ubuntu)
apt [OPTIONS] [COMMAND] (Ubuntu)
The operating system must be updated on a regular basis, this way you will keep your data and integrity of the system safe. In order to update your system, run one of the foll...