apachetop: 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/bin/apachetop - from package: apachetop

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

On Debian possible default full paths are:

/usr/sbin/apachetop - from package: apachetop

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

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