CentOS 6 - Set Static IP

In order to set static ip on CentOS 6:

1. Open ifcfg-Auto_eth0 file at /etc/sysconfig/network-scripts folder
1. sudo vi /etc/sysconfig/network-scripts/ifcfg-Auto_eth0
1. The file name could be different. It could be ifcfg_eth0, too.
2. Change the content to something like below:
1. TYPE=Ethernet
   BOOTPROTO=none
   IPADDR=192.168.11.30
   PREFIX=24
   GATEWAY=192.168.11.1
   DNS1=192.168.11.10
   DNS2=209.18.47.62
   DEFROUTE=yes
   IPV4_FAILURE_FATAL=yes
   IPV6INIT=no
   NAME=eth0
   UUID=06823066-d18a-4af3-b3a0-e2158d152465
   ONBOOT=yes
   HWADDR=00:0C:29:D3:6C:5C
   LAST_CONNECT=1523339343
3. :wq
4. Open resolv.conf and check or correct the nameserver
1. sudo vi /etc/resolv.conf
2. It should be like the following.
1. nameserver 192.168.11.10
2. nameserver 209.18.47.62
5. Restart network
1. sudo /etc/init.d/network restart

Other admins use /etc/sysconfig/network file to specify the default gateway. They may not specify DNS1 or DNS2 in ifcfg-eth0 or ifcfg-Auto_eth0 file. Instead, only the /etc/sysconfig/network file is used to specify the nameservers. 

Below is another example of setting up static ip on CentOS 6

## Configure eth0
#
# vi /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT=yes
HWADDR=A4:BA:CC:37:F1:03
TYPE=Ethernet
BOOTPROTO=static
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
IPADDR=192.168.11.30
NETMASK=255.255.255.0


## Configure Default Gateway
#
# vi /etc/sysconfig/network

NETWORKING=yes
HOSTNAME=centos6
GATEWAY=192.168.11.1


## Restart Network Interface
#

/etc/init.d/network restart

## Configure DNS Server
#
# vi /etc/resolv.conf

nameserver 192.168.11.10      # Replace with your nameserver ip
nameserver 209.18.47.62       # Replace with your nameserver ip

CentOS 6 - Change hostname

To check the host name of CentOS 6,

hostname
hostname -f

To change the host name on CentOS 6,

1. sudo vi /etc/sysconfig/network
1. Update HOSTNAME=[hostname.domain.com] to match the FQDN.
2. For example,
1. HOSTNAME=cent6.contoso.edu
2. :wq
3. If necessary, update /etc/hosts file for internal networking. Change the host that is associated with the IP address.
1. sudo vi /etc/hosts
2. change the host name as needed.
4. Run the hostname command to change the hostname on the server. For example,
1. sudo hostname cent6.contoso.edu
5. Restart network 
1. sudo /etc/init.d/network restart

CentOS 6 - Add a user to sudoers

Here are steps in adding a user to sudoers in CentOS 6

1. Log on as root ( or switch to su with root password).
2. On the command window, do the following.
3. Enter "visudo". 
4. vi loads the sudoer file.
5. Look for %wheel in the sudoer file by entering " /%wheel "
6. Remove # from the line "#  %wheel  ALL=(ALL)  ALL" to enable the wheel group with same privileges as root.
7. Save and exit vi via  :wq.
8. To create a new user:
1. adduser   [new_user_name]
2. passwd    [new_user_name]   [password]
9. Use the usermod command to add the user to the wheel group:
1. usermod   -aG   wheel   [user_name]
10. Switch to the non-root user by entering "su  -  [user_name]"
11. Test by running a command that's allowed for root only.
    For example, /root is generally accessible only by root user. Try listing the content of /root. 
1. sudo  ls  -al  /root