checkpassword: 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:

/bin/checkpassword - from package: fgetty

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

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