checkmk: 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 Debian possible default full paths are:

/usr/bin/checkmk - from package: check

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

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