pcp-atop: 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/libexec/pcp/bin/pcp-atop - from package: pcp-system-tools

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

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