lilypond-book: 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-book - from package: lilypond

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

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