opencv_haartraining: 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/opencv_haartraining - from package: opencv

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

On Debian possible default full paths are:

/usr/bin/opencv_haartraining - from package: libopencv-dev

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

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