nftrack: 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/nftrack - from package: nfdump

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

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