duply: 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 CentOS possible default full paths are:

/usr/bin/duply - from package: duply

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/duply - from package: duply

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

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