conntrack: 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/conntrack - from package: conntrack-tools

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

On Debian possible default full paths are:

/usr/sbin/conntrack - from package: conntrack

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

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