mktexpk: 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/mktexpk - from package: texlive-utils

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

On Debian possible default full paths are:

/usr/bin/mktexpk - from package: texlive-binaries

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

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