interdiff: 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/interdiff - from package: patchutils

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

On Debian possible default full paths are:

/usr/bin/interdiff - from package: patchutils

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

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