devmon: 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/devmon - from package: udevil

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

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