x11perf: 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/x11perf - 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/x11perf - from package: x11-apps

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

Error in other languages:
x11perf: bevel nie gevind nie
x11perf: comandă negăsită
x11perf: comando não encontrado
x11perf: commande introuvable
x11perf: command not found
x11perf: käsku ei ole
x11perf: không tìm thấy lệnh
x11perf: komanda nerasta
x11perf: Kommando nicht gefunden.
x11perf: kommandot finns inte
x11perf: komut yok
x11perf: nie znaleziono polecenia
x11perf: níor aimsíodh an t-ordú
x11perf: no se encontró la orden
x11perf: no s'ha trobat l'ordre
x11perf: opdracht niet gevonden
x11perf: parancs nem található
x11perf: perintah tidak ditemukan
x11perf: príkaz nenájdený
x11perf: příkaz nenalezen
x11perf: команда не найдена
x11perf: командата не е открита
x11perf: 命令找不到
x11perf: コマンドが見つかりません