dvd-slideshow: 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/dvd-slideshow - from package: dvd-slideshow

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