update-maintainer: 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/update-maintainer - from package: ubuntu-dev-tools

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

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