atopd: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/atopd - from package: atop

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