nethogs: 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/nethogs - from package: nethogs

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

On Debian possible default full paths are:

/usr/sbin/nethogs - from package: nethogs

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

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