nfexpire: 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/nfexpire - from package: nfdump

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

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