inputkill: 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/inputkill - from package: watch-maildirs

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

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