density: 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/density - from package: emboss

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

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