tachk: 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 CentOS possible default full paths are:

/usr/bin/tachk - from package: dnssec-tools

You may install the required package with command yum install {package}

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