hardening-check: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/hardening-check - from package: hardening-check

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/hardening-check - from package: hardening-includes

You may install the required package with command apt-get install {package}

Error in other languages:
hardening-check: bevel nie gevind nie
hardening-check: comandă negăsită
hardening-check: comando não encontrado
hardening-check: commande introuvable
hardening-check: command not found
hardening-check: käsku ei ole
hardening-check: không tìm thấy lệnh
hardening-check: komanda nerasta
hardening-check: Kommando nicht gefunden.
hardening-check: kommandot finns inte
hardening-check: komut yok
hardening-check: nie znaleziono polecenia
hardening-check: níor aimsíodh an t-ordú
hardening-check: no se encontró la orden
hardening-check: no s'ha trobat l'ordre
hardening-check: opdracht niet gevonden
hardening-check: parancs nem található
hardening-check: perintah tidak ditemukan
hardening-check: príkaz nenájdený
hardening-check: příkaz nenalezen
hardening-check: команда не найдена
hardening-check: командата не е открита
hardening-check: 命令找不到
hardening-check: コマンドが見つかりません