tcpserver: 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/tcpserver - from package: ucspi-tcp-ipv6
/usr/bin/tcpserver - from package: ucspi-tcp

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

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