nfanon: 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/nfanon - from package: nfdump

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

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