flush: 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/flush - from package: flush

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

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