gammu-smsd-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/gammu-smsd-monitor - from package: gammu-smsd

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

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