idiff: 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/idiff - from package: OpenImageIO-utils

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

On Debian possible default full paths are:

/usr/bin/idiff - from package: openimageio-tools

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

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