calibre-debug: 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/calibre-debug - from package: calibre

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