There are multiple ways to install Telegraf, based on the operating system. The following is a general RPM installation for CentOS or Red Hat:
rpm -ivh https://dl.influxdata.com/telegraf/releases/telegraf-1.7.4-1.x86_64.rpm
For other flavors of Linux, you can refer to the previous docs. Make sure your server has access to the internet to download and install this RPM.