fastadiff: 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/fastadiff - from package: exonerate

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

On Debian possible default full paths are:

/usr/bin/fastadiff - from package: exonerate

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

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