telnetd: 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/kerberos/sbin/telnetd - from package: krb5-appl-servers

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

On Debian possible default full paths are:

/usr/sbin/telnetd - from package: inetutils-telnetd

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

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