duplicity: 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/duplicity - from package: duplicity

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

On Debian possible default full paths are:

/usr/bin/duplicity - from package: duplicity

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

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