certtool: 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/certtool - from package: gnutls-utils

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

On Debian possible default full paths are:

/usr/bin/certtool - from package: gnutls-bin

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

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