x11perfcomp: 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/x11perfcomp - from package: xorg-x11-apps

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

On Debian possible default full paths are:

/usr/bin/x11perfcomp - from package: x11-apps

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

Error in other languages:
x11perfcomp: bevel nie gevind nie
x11perfcomp: comandă negăsită
x11perfcomp: comando não encontrado
x11perfcomp: commande introuvable
x11perfcomp: command not found
x11perfcomp: käsku ei ole
x11perfcomp: không tìm thấy lệnh
x11perfcomp: komanda nerasta
x11perfcomp: Kommando nicht gefunden.
x11perfcomp: kommandot finns inte
x11perfcomp: komut yok
x11perfcomp: nie znaleziono polecenia
x11perfcomp: níor aimsíodh an t-ordú
x11perfcomp: no se encontró la orden
x11perfcomp: no s'ha trobat l'ordre
x11perfcomp: opdracht niet gevonden
x11perfcomp: parancs nem található
x11perfcomp: perintah tidak ditemukan
x11perfcomp: príkaz nenájdený
x11perfcomp: příkaz nenalezen
x11perfcomp: команда не найдена
x11perfcomp: командата не е открита
x11perfcomp: 命令找不到
x11perfcomp: コマンドが見つかりません