postbooks-updater: 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/postbooks-updater - from package: postbooks-updater

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

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