sediff: 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/sediff - from package: setools-console

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

On Debian possible default full paths are:

/usr/bin/sediff - from package: setools

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

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