stencil-twoside: 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/stencil-twoside - from package: piglit

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

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