etop: 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/lib64/erlang/lib/observer-0.9.10/priv/bin/etop - from package: erlang-observer

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

On Debian possible default full paths are:

/usr/lib/erlang/lib/observer-2.0.2/priv/bin/etop - from package: erlang-observer

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

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