mosquitto: 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/sbin/mosquitto - from package: mosquitto

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

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