darcs-monitor: 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/darcs-monitor - from package: darcs-monitor

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

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