lynis: 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/lynis - from package: lynis

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

On Debian possible default full paths are:

/usr/sbin/lynis - from package: lynis

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

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