lddtree: 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/lddtree - from package: pax-utils

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

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