sar: 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
/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/sar - from package: sysstat

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