checkdotdin: 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/checkdotdin - from package: din

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

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