dellLcdBrightness: 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/sbin/dellLcdBrightness - from package: smbios-utils-python

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

On Debian possible default full paths are:

/usr/sbin/dellLcdBrightness - from package: smbios-utils

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

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