netplugd: 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:

/sbin/netplugd - from package: netplug

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

On Debian possible default full paths are:

/sbin/netplugd - from package: netplug

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

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