atopsar: 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/atopsar - from package: atop

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

On Debian possible default full paths are:

/usr/bin/atopsar - from package: atop

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

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