tcpdchk: 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/sbin/tcpdchk - from package: tcpd

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

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