brightside-properties: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/brightside-properties - from package: brightside

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