olpc-brightness: 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/olpc-brightness - from package: olpc-kbdshim

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

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