tkpasswd: 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/tkpasswd - from package: expectk

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

On Debian possible default full paths are:

/usr/bin/tkpasswd - from package: expect

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

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