Starting And Stopping The Server - Red Hat ENTERPRISE LINUX 4 System Administration Manual

The lease database is recreated from time to time so that it is not too large. First, all known leases are
saved in a temporary lease database. The dhcpd.leases file is renamed dhcpd.leases~ and the
temporary lease database is written to dhcpd.leases.
The DHCP daemon could be killed or the system could crash after the lease database has
been renamed to the backup file but before the new file has been written. If this happens, the
dhcpd.leases file does not exist, but it is required to start the service. Do not create a new lease file.
If you do, all old leases are lost which causes many problems. The correct solution is to rename the
dhcpd.leases~ backup file to dhcpd.leases and then start the daemon.

23.2.3. Starting and Stopping the Server

Important
When the DHCP server is started for the first time, it fails unless the dhcpd.leases file
exists. Use the command touch /var/lib/dhcp/dhcpd.leases to create the file if it
does not exist.
If the same server is also running BIND as a DNS server, this step is not necessary, as
starting the named service automatically checks for a dhcpd.leases file.
To start the DHCP service, use the command /sbin/service dhcpd start. To stop the DHCP
server, use the command /sbin/service dhcpd stop.
By default, the DHCP service does not start at boot time. To configure the daemon to start
automatically at boot time, refer to
to manage services.
If more than one network interface is attached to the system, but the DHCP server should only be
started on one of the interfaces, configure the DHCP server to start only on that device. In /etc/
sysconfig/dhcpd, add the name of the interface to the list of DHCPDARGS:
# Command line options here
DHCPDARGS=eth0
This is useful for a firewall machine with two network cards. One network card can be configured as a
DHCP client to retrieve an IP address to the Internet. The other network card can be used as a DHCP
server for the internal network behind the firewall. Specifying only the network card connected to the
internal network makes the system more secure because users can not connect to the daemon via the
Internet.
Other command line options that can be specified in /etc/sysconfig/dhcpd include:
• -p <portnum> — Specify the UDP port number on which dhcpd should listen. The default is port
67. The DHCP server transmits responses to the DHCP clients at a port number one greater than
the UDP port specified. For example, if the default port 67 is used, the server listens on port 67 for
requests and responses to the client on port 68. If a port is specified here and the DHCP relay agent
is used, the same port on which the DHCP relay agent should listen must be specified. Refer to
Section 23.2.4, "DHCP Relay Agent"
• -f — Run the daemon as a foreground process. This is mostly used for debugging.
Chapter 19, Controlling Access to Services
for details.
Starting and Stopping the Server
for information on how
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