postr: 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/postr - from package: postr

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

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