poster: 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/poster - from package: poster

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

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