cdiff: 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/cdiff - from package: colordiff
/usr/lib/ruby/gems/1.8/gems/term-ansicolor-1.0.7/bin/cdiff - from package: rubygem-term-ansicolor

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

On Debian possible default full paths are:

/usr/bin/cdiff - from package: colordiff

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

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