in.talkd: 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/sbin/in.talkd - from package: talk-server

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

On Debian possible default full paths are:

/usr/sbin/in.talkd - from package: talkd

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

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