dhcpd: 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/dhcpd - from package: dhcp

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

On Debian possible default full paths are:

/usr/sbin/dhcpd - from package: isc-dhcp-server-ldap
/usr/sbin/dhcpd - from package: isc-dhcp-server

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

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