frown: 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/frown - from package: frown

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

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