tcpser: 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/tcpser - from package: tcpser

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

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