It’s somewhat likely that your server may already have S.M.A.R.T. installed from some other packages, such as Proxmox, which installs S.M.A.R.T. during its own setup.
To try and see if you’ve already got it installed, just run the command: smartctl -V
If the output is the smartctl version, then you’re all set and good to go, since the package is already installed on your system.
However, if the output is something like “The program ‘smartctl’ is currently not installed”, then you will need to proceed with installing it yourself.
It’s most likely that your linux distro already has this package in its repository, so try installing it that way first:
Ubuntu/Debian: sudo apt install smartmontools
CentOS/Fedora: yum install smartmontools
If you cannot find the package, you can follow the instructions on the S.M.A.R.T. official website on how to proceed with the installation:
https://www.smartmontools.org/wiki/Download