gnome-osd-client: 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/gnome-osd-client - from package: gnome-osd

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

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