tntnet: 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/tntnet - from package: tntnet

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