gendiff: 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/gendiff - from package: rpm-build

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

On Debian possible default full paths are:

/usr/bin/gendiff - from package: rpm

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

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