clear-accum: 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/lib64/piglit/bin/clear-accum - from package: piglit

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

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