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Details
Redhat / CentOS
The conventional way used to change runlevel using /etc/inittab has become obsolete with Redhat Enterprise Linux version 7. As a result any Linux system using systemd system management daemon now relies on systemctl command to change runlevel or to be more precise to change the target. As a result any edits of /etc/inittab file will not take effect on RHEL 7. The term runlevel still exists on RHEL 7 and we cat check current runlevel using runlevel command: 
[root@rhel7 ~]# runlevel 
N 3

Details
Redhat / CentOS
If you have performend a RHEL 7 Linux Server installation and did not include Graphical User Interface (GUI) you can do it later directly from command line using yum command and selecting an appropriate installation group. To list all available installation groups on Redhat 7 Linux use: 
[root@rhel7 ~]# yum group list
Loaded plugins: product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
There is no installed groups file.
Maybe run: yum groups mark convert (see man yum)
Available environment groups:
   Minimal Install
   Infrastructure Server
   File and Print Server
   Basic Web Server
   Virtualization Host
   Server with GUI
Available Groups:
   Compatibility Libraries
   Console Internet Tools
   Development Tools
   Graphical Administration Tools
   Legacy UNIX Compatibility
   Scientific Support
   Security Tools
   Smart Card Support
   System Administration Tools
   System Management
Done

Details
Redhat / CentOS
Depending on your Rendhat 7 installation you may end up with a default hostname localhost.localdomain. This hostname will be shown on various services your new server will offer as well a it will be show on your command prompt such us: 
[root@localhost ~]#
To change your hostname simply edit vi /etc/hostname file and inlcude name of your host.

Details
Redhat / CentOS
The error message bellow will be display on your Redhat 7 linux system after a fresh RHEL 7 system installation. It simply means that in order to get system updates and also to install new software you need to configure package repositories. 
Loaded plugins: product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
There are no enabled repos.
 Run "yum repolist all" to see the repos you have.
 You can enable repos with yum-config-manager --enable

Details
Redhat / CentOS
On Redhat Linux system's the ifconfig command to display system IP address has become obsolete. Currently, to view an IP address on your RHEL 7 system enter the following linux command: 
# ip addr show
OR
# ip a s
2: enp0s3:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:15:38:b7 brd ff:ff:ff:ff:ff:ff
    inet 10.1.1.110/8 brd 10.255.255.255 scope global enp0s3
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe15:38b7/64 scope link 
       valid_lft forever preferred_lft forever

Details
Redhat / CentOS
systemctl command is used on RedHat 7 linux to manage services system wide. It allows administrators to manage ssh service to start, restart, stop or enable autoload after system startup. In install ssh service on your RHEL 7 linux run a following linux command: 
# yum install openssh
By defalt SSH service or to be more precise sshd ( daemon ) is disabled. Once the opensshd package installed, you can check the status of SSHD service by using the below command: 
# systemctl status sshd
sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; disabled)
   Active: inactive (dead)
To start ssh daemon (sshd) on RHEL 7 run: 
systemctl start sshd

Details
Redhat / CentOS
Below are basic configuration instructions to setup static IP address on Redhat Enterprise Linux ( RHEL7 ). First, list your network interfaces with ip command: 
# ip addr show
2: enp0s3:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:15:38:b7 brd ff:ff:ff:ff:ff:ff
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe15:38b7/64 scope link 
       valid_lft forever preferred_lft forever

Details
Redhat / CentOS

Introduction

Logrotate is a utility designed for administrators who manage servers producing a high volume of log files to help them save some disk space as well as to avoid a potential risk making a system unresponsive due to the lack of disk space. Normally, a solution to avoid this kind of problem is to setup a separate partition or logical volume for a /var mount point. However, logrotate may also be a viable solution to this problem especially if it is too late to move all logs under different partition. In this article we will talk about usage and configuration of logrotate on RedHat / CentOS Linux server.

What is Logrotate

Logrotate provides an ability for a system administrator to systematically rotate and archive any log files produced by the system and thus reducing a operating system's disk space requirement. By default logrotate is invoked once a day using a cron scheduler from location /etc/cron.daily/

# ls /etc/cron.daily/
cups  logrotate  makewhatis.cron  mlocate.cron  prelink  readahead.cron  rhsmd  tmpwatch

Details
Redhat / CentOS
If you have a missing default gateway on your Redhat system you can add new route as per network interface or globally. Defining default gateway using ifcfg files, that is, defining it as per network interface basis takes a precedence over global system wide default gateway configuration defined by /etc/sysconfig/network configuration file.

First, list our routing table with routel command: 
[root@rhel7 ~]# routel
         target            gateway          source    proto    scope    dev tbl
      10.0.0.0/ 8                        10.1.1.56   kernel     link enp0s3 
       10.0.0.0          broadcast       10.1.1.56   kernel     link enp0s3 local
      10.1.1.56              local       10.1.1.56   kernel     host enp0s3 local
 10.255.255.255          broadcast       10.1.1.56   kernel     link enp0s3 local
      127.0.0.0          broadcast       127.0.0.1   kernel     link     lo local
     127.0.0.0/ 8            local       127.0.0.1   kernel     host     lo local
      127.0.0.1              local       127.0.0.1   kernel     host     lo local
127.255.255.255          broadcast       127.0.0.1   kernel     link     lo local

Details
Redhat / CentOS
Apart of the regular local Redhat's installation, the Redhat system allows admin to modify boot options to temporarily setup network interface and instruct the installation program Anaconda to initiate installation via VNC. In this article we will modify default Redhat's boot options to initiate remote installation using VNC.

First insert installation image and boot into a Redhat's boot options screen as show below:

Redhat 7 boot screen - enter vnc and network options

On this screen we need to modify boot options to instruct the installation program Anaconda to provide us with VNC interface after the end of the boot sequence. Depending whether you use DHCP on your network you can either set static address or do not include any network options for dynamic IP address assignment. In the above screen we have included the following options after pressing "TAB" on the main ( first ) boot option: 
ip=10.1.1.56 - optional
netmask=255.0.0.0 - optional
vnc - required

Details
Redhat / CentOS

Introduction

Most of the time as a system administrator you are managing your servers over the network. It is very rare that you will need to have a physical access to any of your managed servers. In most cases all you need is to SSH remotely to do your administration tasks. In this article we will configure a GUI alternative to a remote access to your RHEL server, which is VNC. VNC allows you to open a remote GUI session to your server and thus providing you with a full graphical interface accessible from any remote location.

Installation of VNC server

In order to enable an access to our Redhat Linux system using VNC we first need to install it. Make sure that you have your repository enabled and execute the command:

# yum install tigervnc-server

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