opennx: 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:

/opt/opennx/bin/opennx - from package: opennx

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

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