Configuring DHCP Server in RHEL7/ Cent OS 7

DHCP – Dynamic host configuration protocol

We are going to configure DHCP Server in RHEL7

It’s a network protocol used to assign IP’s to the client dynamically over the network.

DHCP Workflow:

Required Package installation:

#yum install dhcp

Now we should assign a insterface in DHCPDARGS in /etc/sysconfig/dhcpd

 [[email protected] ~]# vi /etc/sysconfig/dhcpd
 
  DHCPDARGS=enp0s3

After installing package it will create one empty configuration file /etc/dhcp/dhcpd.conf  and we have one sample configuration file under /usr/share/doc/dhcp-4.2.15/dhcpd.conf.exmaple.

So as first, append the content from example file to original file using cat command.

[[email protected] ~]# cat /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example >> /etc/dhcp/dhcpd.conf

Open the configuration file to configure DHCP Server:

First will give basic configuration which will be common for your network.

[[email protected] ~]# vi /etc/dhcp/dhcpd.conf


Make the below entries 

 option domain-name "lbcdomain.com";
 option domain-name-servers server.lbcdomain.com;
 default-lease-time 600;
 max-lease-time 7200;
 authoritative;
 log-facility local7;



Now make subnet details in same configuration file.

subnet 192.168.1.0 netmask 255.255.255.0 {
 option routers 192.168.1.254;
 option subnet-mask 255.255.255.0;
 option domain-search "lbcdomain.com";
 option domain-name-servers 192.168.1.1;
 option time-offset -18000; # Eastern Standard Time
 range 192.168.1.10 192.168.1.100;
}

Optional(To reserve IP for a dhcp client machine) :

If you wan to assign a static IP to a client using DHCP service, use the below command.

host station1 {
 option host-name "node11.lbcdomain.com";
 hardware ethernet 00:12:2A:2B:3C:AB;
 fixed-address 192.168.1.100;
}

Restart the dhcp service now to complete the DHCP server configuration.

[[email protected] ~]# systemctl restart dhcp
To check dhcp we should login in client machine which is in same network physically and edit the interface configuration file to make dhcp ip assigned.
#vi /etc/sysconfig/network-scripts/ifcfg-eth0
 change the entry for BOOTPROTO as dhcp

DEVICE=eth0

BOOTPROTO=dhcp

TYPE=Ethernet

ONBOOT=yes
 
Save and quit.
 
Now restart the network service.
 #service network restart
 
now check for the ip and it should be assigned in between 192. 168.1.50 to 192.168.1.254
  
DHCP Configuration has been done.
Do practice well. All the best.

Changing/ Recovering root user password in RHEL7/ Cent OS 7

We are going to see How to Changing/ Recovering root user password in RHEL7/ CentOS 7 in this post

Boot the system and wait for GRUB menu. On some Operating systems, you need to disturb the booting by pressing any keys in your system.

Changing/ Recovering root user password in RHEL7/ Cent OS 7
Highlight the first line which is pointing the Operating System entry like showed in the above image and press “e” key in your keyboard to edit manually.
Then will get the below screen.
Using up/down, left/right arrow keys move the cursor to the “rhgb quiet” which is in kernel line starting with “linux16”
Using delete/backspace keys manually delete “rhgb quiet” entry and append “init=/bin/bash” entry like below.

Than press Ctrl+x  to reboot your OS with specified option. Once rebooted, will get a shell prompt without credentials.

check whether the root filesystem has been mounted or not.

Mount the root filesystem with RW permission.

Now issue the “passwd” command to recover/change the root password. It will ask for the new password and re-enter the password for confirmation. Once provided the new password will receive the “Authentication token successfully updated”

Relabel the SELinux content using below command.
Restart the machine using the below command.
Finally, we recovered the root password. Now will restart the machine and login with a new root password.

Configuring LVM in redhat

For LVM Configuration need to follw the below steps.

1. Partition creation
2. Physical volume creation
3. Volume group creation
4. Logical volume creation

Here i’m using /dev/sda and /dev/sdb hard disks

Size:

/dev/sda – 500GB
/dev/sdb – 500GB

I already shared the steps to create partitions in previous post.

Click here to create new partition/filesystem in a physical disk.

Using fdisk we have to change the partition type by changing the ID.

For that we should use “t” option to change the partition type. Once we executed this, it will ask for
the Hex code of partition type. Here we need to mention “8e” as Hex code for LVM partition type.

Note: change the partition type for all HDD/ Partitions which we are going to configure LVM.

Than follow the below steps for LVM configuration.

Next we have to create physical volumes using below mentioned commands.

#pvcreate /dev/sda1 /dev/sdb1


#vgcreate -s 16M newvg /dev/sda1 /dev/sdb1

“newvg” is new volume group name and /dev/sda1, /dev/sdb1 will be added in this volume group.
Now this two hard disks will act as a single hard disk and the new size of hard disk is 1000GB.

Next we have to create logical volumes over the volume group, which is like a partitioning here.

#lvcreate -n lv1 -L 200G newvg

-n:  This option is to mention the new logical volume group.
lv1: new logical volume group name.
-L:  this option is to mention the size of new logical volume.

Now we have created logical volume and we should format and mount the lv.

#mkfs.xfs /dev/newvg/lv1

directory is required to mount the lv.

#mkdir /data

#mount /dev/newvg/lv1 /data


Now we successfully configured LVM. Follow the lvcreate steps to create more lv’s.