nfsref: 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/sbin/nfsref - from package: fedfs-utils-server

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

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