The commands to check CentOS version

The following table contains most common and recommended ways on how to check CentOS version on your CentOS Linux server or desktop.

CommandDescription
$ rpm -q centos-releaseCentOS version valid for CentOS 6 and higher. Causes to reveal major, minor and asynchronous CentOS version.
$ lsb_release -dRequires redhat-lsb package to be installed before execution.
$ rpm -E %{rhel}RPM macro to reveal a major CentOS version
$ rpm –eval %{centos_ver}RPM macro to display a major version of CentOS
$ cat /etc/centos-releaseLinux cat command to output content of the /etc/centos-release to query CentOS version. Works with CentOS 6 and higher.

In case the above-provided commands did not help you to obtain the CentOS version number you may try the following alternative commands.

Although available only for CentOS version 7 and above the hostnamectl command might provide you with a significant clue about your OS version number:

$ hostnamectl 
   Static hostname: localhost.localdomain
         Icon name: computer-vm
           Chassis: vm
        Machine ID: fe069af6a1764e07be909d7cf64add99
           Boot ID: b81bb73dc549484c8927e830e149eb55
    Virtualization: kvm
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-862.6.3.el7.x86_64
      Architecture: x86-64

For more answers try to query all release files within the /etc directory:

$ cat /etc/*elease
CentOS Linux release 7.5.1804 (Core) 
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"

CentOS Linux release 7.5.1804 (Core) 
CentOS Linux release 7.5.1804 (Core)

Bash Script to check CentOS version

The following bash script can be used to obtain the CentOS version number given that the /etc/centos-release file exists and is populated.

The below script serves as an example, feel free to modify wherever appropriate. For more information about Bash Scripting visit our bash scripting tutorial:

#!/bin/bash

full=`cat /etc/centos-release | tr -dc '0-9.'`
major=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f1)
minor=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f2)
asynchronous=$(cat /etc/centos-release | tr -dc '0-9.'|cut -d \. -f3)

echo CentOS Version: $full
echo Major Relase: $major
echo Minor Relase: $minor
echo Asynchronous Relase: $asynchronous

Output:

$ ./check-centos-version.sh 
CentOS Version: 7.5.1804
Major Relase: 7
Minor Relase: 5
Asynchronous Relase: 1804

Python program to check CentOS version

The following python script will output the distribution name along with the OS version number:

#!/usr/bin/python

import platform
print platform.linux_distribution()

Alternatively, one can execute python code directly from the shell:

$ python -c 'import platform; print platform.linux_distribution()'

Output:

$ python check-centos-version.py 
('CentOS Linux', '7.5.1804', 'Core')

How to generate linux server certificates

  1. Generate a Private Key
openssl genrsa -des3 -out server.key 1024
  1. Generate a CSR (Certificate Signing Request)
openssl req -new -key server.key -out server.csr
  1. Remove Passphrase from Key
cp server.key server.key.org
openssl rsa -in server.key.org -out server.key
  1. Generating a Self-Signed Certificate
openssl x509 -req -days 1365 -in server.csr -signkey server.key -out server.crt
  1. Installing the Private Key and Certificate
cp server.crt /etc/pki/tls/certs/ssl.crt
cp server.key /etc/pki/tls/private/ssl.key

 

Fail2ban Status commands

fail2ban-client status postfix

Show status of all fail2ban jails at once
create the file fail2ban-allstatus.sh
#!/bin/bash
JAILS=`fail2ban-client status | grep Jail list | sed -E s/^[^:]+:[ \t]+// | sed s/,//g`
for JAIL in $JAILS
do
fail2ban-client status $JAIL
done

or with a command

fail2ban-client status|awk -F: ‘/Jail list:/ { split($2,jail,”,”) ; for (i in jail) { gsub(/[\t ]/,””,jail[i]); system(“fail2ban-client status “jail[i]); }; }’

grep -srni “journalmatch” /etc/fail2ban/filter.d/

 

Yum warning

After a yum update I receive this worning :

warning: /etc/fail2ban/jail.conf created as /etc/fail2ban/jail.conf.rpmnew

Those warnings are expected if you have made changes to your configuration files. yum is kind enough to not overwrite your existing modified configuration, but instead writes the new default configuration file to a .rpmnew file, which you can then review and perhaps incorporate the new defaults etc to your own configuration. This is OK. The kernel module warnings are also of no concern.

 

How to Use Virtual Environments

Useful command for python system environment or custom environment.
When any environment is not activated you are using the system environment.
pip list
pip3 list
create new environment :
python3 -m venv env_name
create a directory env_name
activate the env_name :
source env_name/bin/activate
show which python :
which python
deactivate environment :
deactivate
create an environment with the same packages of the system environment :
python3 -m venv env_name –system-site-packages
how to show the only packages installed in the env_name environment
pip list –local