gtkperf: 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 Debian possible default full paths are:

/usr/bin/gtkperf - from package: gtkperf

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

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