lilypond: 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/lilypond - from package: lilypond

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

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