Introduction

lsof command meaning “List open files“. This command will not find CentOS7/RHEL. We will install lsof command example as below:

$ sudo yum install lsof

In the realm of Linux administration, understanding the tools at your disposal is key to effective system management. The lsof command, which stands for “List Open Files”, is an indispensable utility that provides crucial visibility into the system’s file usage. By listing information about files opened by processes, lsof helps administrators manage resources, troubleshoot system issues, and ensure secure operations. This guide aims to demystify the lsof command through practical examples, enhancing your system management toolkit.

Basic Usage

lsof

This will display a list of all open files and the processes that are using them.

lsof command examples

List open files

$ lsof -n

Kill a process running on port 8443

$ lsof -i :8443 | awk '{print $2}' | tail -n 1 | xargs kill
# or
$ lsof -i :8443  | awk 'NR > 1 {print $2}' | xargs --no-run-if-empty kill

Show the 15 Largest Open Files in Linux.

$ lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB" " " $9 " " $1 }' | sort -n -u | tail -n 15

List User-Specific Opened Files. This will display a list of all open files that are being used by the specified user.

$ lsof -u huupv

Search by PID

$ lsof -p 1

Exclude User with ^ Character

$ lsof -i -u^root

List TCP Port ranges 8000-9000

$ lsof -i TCP:8000-9000

Conclusion

The lsof command is a powerful tool in the Linux administrator’s arsenal, offering deep insights into the system’s interaction with files. From tracking down process-specific files to managing system resources, lsof facilitates a wide range of administrative tasks.

By mastering its usage through the examples provided, you enhance your capabilities in system management, contributing to the overall efficiency and security of your operations. Dive into these examples to leverage lsof effectively, ensuring your Linux systems run smoothly and securely. I hope will this your helpful. Thank you for reading the DevopsRoles page!

#Introduction

In this tutorial, How To Install Apache cassandra on Centos 6. Apache Cassandra is a NoSQL database for storing large amounts of data in a decentralized, high availability server cluster.

Step 1: Install Java

I will install Oracle java 7 instead of OpenJDK. Link download Oracle Java 7 here

rpm -ivh /home/huupv/jdk-7u79-linux-x64.rpm

I find both executable files – OpenJDK and Oracle:

find / -name "java" -type f

Check java version

java -version

Setting up the default JDK

alternatives --config java

Step 2: Install Apache cassandra

Cassandra will be installed from the Datastax repository. Create a repository file:/etc/yum.repos.d/datastax.repo

[datastax]
name = DataStax Repo for Apache Cassandra
baseurl = http://rpm.datastax.com/community
enabled = 1
gpgcheck = 0

Find the version

yum list dsc2*

Install

yum install dsc21

Start and add to the auto-launch:

service cassandra start
chkconfig cassandra on

Check

cqlsh
nodetool status

Conclusion

You have to Install Apache Cassandra on Centos 6. I hope will this your helpful. Thank you for reading the DevopsRoles page!

Introduction

In this tutorial, How to automatically mount a SMB/CIFS Share on CentOS.

Prerequisite

Install necessary packages

yum install samba-client samba-common

Automatically mount a SMB/CIFS Share on CentOS

Install the Automounter

yum install autofs

Create a mount point

mkdir /data/cifs_share

Add an entry to the file /etc/auto.master, as follow:

/data/cifs_share /etc/auto.cifs  --timeout=600 --ghost

create the file /etc/auto.cifs:

share_data -fstype=cifs,rw,noperm,credentials=/etc/credentials.txt
    ://<Host Name>/<Folder Name>

Create /etc/credentials.txt file

username=DOMAIN/User
password=PASSWORD

Secure the credentials.txt file

chmod 0700 /etc/credentials.txt

Restart the automounter service

/etc/init.d/autofs restart

Confirm that the mount is being accessed correctly

mount

Conclusion

You have automatically mounted an SMB/CIFS Share on CentOS. I hope will this your helpful. Thank you for reading the DevopsRoles page!

#Introduction

In this tutorial, How to install Let’s Encrypt SSL on CentOS 7. Let’s Encrypt is a free, automated TLS/SSL certificate web server. In the previous post, I have installed Let’s Encrypt SSL on Centos 6 here.

Prerequisite

yum install -y epel-release mod_ssl

How to install Let’s Encrypt SSL on CentOS 7

yum install -y certbot

Generate a SSL certificate

sudo certbot certonly \
--manual \
--agree-tos \
--preferred-challenges=dns \
--server https://acme-v02.api.letsencrypt.org/directory \
--email huupv@devopsroles.com \
--domains devopsroles.com

Certificated will be available under the folder: /etc/letsencrypt/live/devopsroles.com

/etc/letsencrypt/live/devopsroles.com/fullchain.pem
/etc/letsencrypt/live/devopsroles.com/privkey.pem

Create SystemD service for certbot.service. New file /etc/systemd/system/certbot.service

[Unit]
Description=Renew Let's Encrypt certificates
After=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/bin/certbot renew --renew-hook "/bin/systemctl --no-block reload nginx" --quiet --agree-tos

Create SystemD service for certbot.timer. New file /etc/systemd/system/certbot.timer

[Unit]
Description=Daily renewal of Let's Encrypt's certificates

[Timer]
OnCalendar=daily
RandomizedDelaySec=1day
Persistent=true

[Install]
WantedBy=timers.target

Start and enable certbot.timer

systemctl daemon-reload
systemctl start certbot.timer
systemctl enable certbot.timer

List service certbot timer as follow

systemctl list-timers certbot.timer

Conclusion

You have installed Let’s Encrypt SSL on CentOS 7. I hope will this your helpful. Thank you for reading the DevopsRoles page!

#Introduction

In this tutorial, How to install Let’s Encrypt SSL on CentOS 6. Let’s Encrypt is a free, automated TLS/SSL certificate web server.

Prerequisite

Your server has installed a Web server If it’s not then you can use the command to install a web server

For Nginx

# yum install nginx

For Apache

# yum install httpd mod_ssl

Install LetsEncrypt on Centos 6

curl -o /usr/local/sbin/certbot-auto https://dl.eff.org/certbot-auto
chmod a+x /usr/local/sbin/certbot-auto

Generate a SSL certificate

sudo /usr/local/sbin/certbot-auto certonly \
--manual \
--agree-tos \
--preferred-challenges=dns \
--server https://acme-v02.api.letsencrypt.org/directory \
--email huupv@devopsroles.com \
--domains devopsroles.com

certificated will be available under the folder: /etc/letsencrypt/live/devopsroles.com

/etc/letsencrypt/live/devopsroles.com/fullchain.pem
/etc/letsencrypt/live/devopsroles.com/privkey.pem

Setup a cron job for Let’s Encrypt SSL

# Setting up crontab
crontab -e

# Append the below line to the end of crontab
0 0 * * * /usr/local/sbin/certbot-auto renew --renew-hook "/sbin/service nginx reload" --quiet --agree-tos

HOW TO SETUP NGINX TO USE SSL WITH LETSENCRYPT

For example, as follow

server {
 listen 443;
 ssl on;
 server_name devopsroles.com;
 ssl_certificate /etc/letsencrypt/live/devopsroles.com/fullchain.pem;
 ssl_certificate_key /etc/letsencrypt/live/devopsroles.com/privkey.pem;
 root /etc/nginx/html;
 
}

Conclusion

You have installed Let’s Encrypt SSL on CentOS 6. I hope will this your helpful. Thank you for reading the DevopsRoles page!

#Introduction

In this tutorial, How to build a repository use nexus repository. In the previous post, I have installed the Nexus repository here.

Maven build a repository with Nexus Repository

Hosted repository

Create a new repository as below:

Name: maven2-hosted

proxy repository

Create a new proxy repository as below

• Name: maven2-proxy
• Remote storage: https://repo1.maven.org/maven2/

group repository

Create a new group repository as below

• Name: maven2-group
• Members: maven2-private-example maven2-proxy-example

How to get package from Nexus Repository

I will create a maven project in eclipse.

Edit the pom.xml file. I will get a poi package.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>nexus-devopsroles</groupId>
  <artifactId>maven2</artifactId>
  <version>0.0.1-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>poi</groupId>
            <artifactId>poi</artifactId>
            <version>2.5.1</version>
        </dependency>
    </dependencies>

    <repositories>
        <repository>
            <id>maven-group</id>
            <name>My Maven Group Repository</name>
            <url>http://192.168.3.4:8081/repository/maven2-group/</url>
            <releases>
                <enabled>true</enabled>
            </releases>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>

    <pluginRepositories>
        <pluginRepository>
            <id>maven-group</id>
            <name>My Maven Group Repository</name>
            <url>http://192.168.3.4:8081/repository/maven2-group/</url>
        </pluginRepository>
    </pluginRepositories>

    <distributionManagement>
        <repository>
            <id>maven2-private-example</id>
            <name>My Maven Hosted Repository</name>
            <url>http://192.168.3.4:8081/repository/maven2-private-example/</url>
        </repository>
    </distributionManagement>
</project>

Maven does not download packages that have already been acquired from the web, so packages are not stored in the proxy repository

NPM build a repository with Nexus Repository

Hosted repository

Create a new repository as below

Name: npm-hosted

proxy repository

Create a new proxy repository as below

• Name: npm-proxy-example
• Remote storage: https://registry.npmjs.org

group repository

Create a new group repository as below

• Name: npm-group
• Members: npm-proxy-example npm-private-example

How to get the package

Create the following two files in any directory

.npmrc file

email=HuuPV@devopsroles.com
always-auth=true
_auth=YWRtaW46YWRtaW4xMjMxMjM=

registry=http://192.168.3.4:8081/repository/npm-proxy/

package.json file

{
  "name": "npm-hosted",
  "version": "1.0.0",
  "description": "for nexus3",
  "dependencies": {
  }
}

Authentication information generated by the following method

echo -n 'admin:admin123123' | openssl base64

Output

YWRtaW46YWRtaW4xMjMxMjM=

Get the required packages from a repository on the Internet via the Nexus3 proxy repository. By acquiring via the proxy repository, it is automatically saved to Nexus3 as well as downloaded.

npm install --save <package name>
# Example
npm install --save bower

As a result of executing the above command, the package is saved.

Conclusion

You have to Build a repository use Nexus Repository. I hope will this your helpful. Thank you for reading the DevopsRoles page!

#Introduction

In this tutorial, How to Install Nexus Repository OSS on CentOS 7. There are three types of Nexus3 repositories.

• A hosted repository that constitutes a repository by itself.
• Proxy repository that relays access to another repository.
• Group repository that aggregates hosted and proxy.

Prerequisites

yum install -y epel-release unzip vim wget net-tools
yum -y install java-1.8.0-openjdk java-1.8.0-openjdk-devel

Disable SELinux on Centos as follows

[root@DevopsRoles ~]# cat /etc/sysconfig/selinux

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=disabled
# SELINUXTYPE= can take one of three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected.
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

Install Nexus Repository OSS on Centos 7

# Creating necessory folder structure
mkdir -p /Data/nexus-data /opt/nexus

# Download latest Nexus artifact
wget -O /tmp/nexus.tar.gz http://download.sonatype.com/nexus/3/latest-unix.tar.gz

# Extract it to /opt/nexus
tar xvfz /tmp/nexus.tar.gz -C /opt/nexus --strip-components 1

# Adding a service account for nexus
useradd --system --no-create-home nexus

# Provide necessory folder permissions
chown -R nexus:nexus /opt/nexus
chown -R nexus:nexus /Data/nexus-data

Configure environment for Nexus repository OSS on CentOS 7

# Setting up the default JDK
alternatives --config java 

# Setting up JAVA_HOME and NEXUS_HOME
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-0.el7_8.x86_64
export NEXUS_HOME=/opt/nexus
source /etc/bashrc

# Check the JAVA version
java -version

Change Nexus default values as follows

[root@DevopsRoles ~]# cat $NEXUS_HOME/bin/nexus.vmoptions
-Xms1200M
-Xmx1200M
-XX:MaxDirectMemorySize=4G
-XX:+UnlockDiagnosticVMOptions
-XX:+UnsyncloadClass
-XX:+LogVMOutput
-XX:LogFile=/Data/nexus-data/nexus3/log/jvm.log
-Djava.net.preferIPv4Stack=true
-Dkaraf.home=.
-Dkaraf.base=.
-Dkaraf.etc=etc/karaf
-Djava.util.logging.config.file=etc/karaf/java.util.logging.properties
-Dkaraf.data=/Data/nexus-data/nexus3
-Djava.io.tmpdir=/Data/nexus-data/nexus3/tmp
-Dkaraf.startLocalConsole=false

#
# additional vmoptions needed for Java9+
#
# --add-reads=java.xml=java.logging
# --add-exports=java.base/org.apache.karaf.specs.locator=java.xml,ALL-UNNAMED
# --patch-module=java.base=lib/endorsed/org.apache.karaf.specs.locator-4.2.9.jar
# --patch-module=java.xml=lib/endorsed/org.apache.karaf.specs.java.xml-4.2.9.jar
# --add-opens=java.base/java.security=ALL-UNNAMED
# --add-opens=java.base/java.net=ALL-UNNAMED
# --add-opens=java.base/java.lang=ALL-UNNAMED
# --add-opens=java.base/java.util=ALL-UNNAMED
# --add-opens=java.naming/javax.naming.spi=ALL-UNNAMED
# --add-opens=java.rmi/sun.rmi.transport.tcp=ALL-UNNAMED
# --add-exports=java.base/sun.net.www.protocol.http=ALL-UNNAMED
# --add-exports=java.base/sun.net.www.protocol.https=ALL-UNNAMED
# --add-exports=java.base/sun.net.www.protocol.jar=ALL-UNNAMED
# --add-exports=jdk.xml.dom/org.w3c.dom.html=ALL-UNNAMED
# --add-exports=jdk.naming.rmi/com.sun.jndi.url.rmi=ALL-UNNAMED
#
# comment out this vmoption when using Java9+
#
-Djava.endorsed.dirs=lib/endorsed

Configure application-host as follows

[root@DevopsRoles ~]# cat $NEXUS_HOME/etc/nexus-default.properties
## DO NOT EDIT - CUSTOMIZATIONS BELONG IN $data-dir/etc/nexus.properties
##
# Jetty section
application-port=8081
application-host=192.168.3.4
nexus-args=${jetty.etc}/jetty.xml,${jetty.etc}/jetty-http.xml,${jetty.etc}/jetty-requestlog.xml
nexus-context-path=/

# Nexus section
nexus-edition=nexus-pro-edition
nexus-features=\
 nexus-pro-feature

nexus.hazelcast.discovery.isEnabled=true

Configure the nexus service account

[root@DevopsRoles ~]# cat $NEXUS_HOME/bin/nexus.rc
#run_as_user=""
run_as_user="nexus"

Create SystemD service as follows

[root@DevopsRoles ~]# cat /etc/systemd/system/nexus.service
[Unit]
Description=Nexus Server
After=syslog.target network.target

[Service]
Type=forking
LimitNOFILE=65536
ExecStart=/opt/nexus/bin/nexus start
ExecStop=/opt/nexus/bin/nexus stop
User=nexus
Group=nexus
Restart=on-failure

[Install]
WantedBy=multi-user.target

Increasing the open file limit of nexus user

[root@DevopsRoles ~]# grep nexus /etc/security/limits.conf
nexus    -    nofile    65536

Start and Enable Nexus service

systemctl daemon-reload
systemctl start nexus.service
systemctl enable nexus.service

Check nexus service is running

netstat -npltu | grep 8081

Nexus log files for issues

tail -f /Data/nexus-data/nexus3/log/nexus.log

Nexus Initial Login Information

• URL: http://192.168.3.4:8081
• User: admin
• Password: admin123

Conclusion

You have to Install Nexus Repository OSS and configure Nexus Repository OSS on CentOS 7. I hope will this your helpful. Thank you for reading the DevopsRoles page!