writebuffer: 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
/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/writebuffer - from package: chiark-rwbuffer

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