diffuse: 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/diffuse - from package: diffuse

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

On Debian possible default full paths are:

/usr/bin/diffuse - from package: diffuse

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

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