dhcp_lease_time: 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/dhcp_lease_time - from package: dnsmasq-utils

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

On Debian possible default full paths are:

/usr/bin/dhcp_lease_time - from package: dnsmasq-utils

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

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