CentOS

Introduction

CentOS is a GNU/Linux operating system with long term support (10 years after release). It is a rebuild of Red Hat Enterprise Linux. Some packages in the distribution are already 1 to 2 years old when a new CentOS release is made. That means you don't get the most current software, but the software you get is quite mature. You can assume that most of the bugs in every software in CentOS have been found and fixed already. Anyway, there's sometimes a route to newer software, for example, very new kernels can be installed.

Just one comparison:

• Linux kernel: When CentOS 7 was released on 2014-07-07, it was shipped with Linux 3.10. At this time, this kernel was already one year old (released by the end of June, 2013). Ubuntu 14.04, which was released in April, 2014, already contained Linux 3.13.

CentOS@Distrowatch

Setting up

Setting up network and network tools

If there is no network connectivity, the network might be unconfigured. Get an IP address by issuing

dhclient enp0s3

Adjust enp0s3 to your needs!

If you don't know the names of your network interfaces, this command will tell them to you:

cat /proc/net/dev

The network configuration is saved in /etc/sysconfig/network-scripts: each network interface has got a file ifcfg-name, for example "ifcfg-enp0s3" for an ethernet adapter. In such a file, "ONBOOT=yes" can be set, so the interface will be brought up at boot. See also: Network Configuration Files

CentOS 7

After that, install some basic network utilities:

yum install ntp ntpdate ntp-doc net-tools

The "net-tools" package includes "netstat" and "ifconfig".

These commands enable and start the network time daemon:

systemctl enable ntpd
systemctl start ntpd

CentOS 8

timedatectl set-ntp 1

This activates time synchronisation.

Software

CentOS uses the yum command to manage its packages. The most important commands are:

yum install package
yum remove package
yum list
yum provides command
yum search package

Many more options can be seen in its man page.

Comparing to "apt" in Debian/Ubuntu, yum is slightly slower than apt, because at every start it outputs something like

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 base: artfiles.org
 elrepo: nl.mirror.babylon.network
 epel: nl.mirror.babylon.network
 extras: ftp.plusline.de
 updates: mirror.dataone.nl

However, I would not perceive that as a problem. Until now, yum never made troubles and did a fantastic job.

Install EPEL

To do some advanced things, like vnstat or lxc, install epel-release:

yum install epel-release

Enabling automatic updates

yum -y install yum-cron
systemctl enable yum-cron
systemctl start yum-cron

It is recommended to review the settings using

nano /etc/yum/yum-cron.conf

Installing and configuring vnstat

yum install vnstat
systemctl enable vnstat
systemctl start vnstat

Then, for every interface that ifconfig | grep "RUNNING" reports, create the database by using

sudo -u vnstat vnstat -i -u iface

It is important to run this as user "vnstat" so the database files in /var/lib/vnstat/ have the right permissions (rw-r--r-- or 644) and owner (vnstat.vnstat). The daemon that updates the database files runs as user "vnstat" and if the files are not writeable by this user, the daemon cannot do its job.

After every interface added, the daemon must be restarted so it is notified about that change:

systemctl restart vnstat

LXC

Installing LXC

Linux containers can be used when installing these packages:

yum install lxc lxc-templates debootstrap perl libvirt lxc-extra
systemctl enable lxc
systemctl start lxc
systemctl start libvirtd

Credits

debootstrap is for installing Debian and operating systems based on it (like Ubuntu). lxc-extra contains the lxc-ls command (which is actually just a python script).

There is a how to that explains how LXC can be installed on CentOS when using libvirt and friends.

Creating a CentOS container

lxc-create -t download -n centos8c1 -- -d centos -r 8 -a amd64

Installing recent kernel

rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm
yum --enablerepo=elrepo-kernel install kernel-ml

Credits