masked-clear: 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/masked-clear - from package: piglit

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

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