readbuffer: 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/readbuffer - from package: chiark-rwbuffer

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

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