Master Linux: From Installation to Advanced System Management

Why Learn Linux

Windows is commercial, becomes slower over time, and is prone to viruses; Linux is free, open‑source, runs stably for long periods, and virtually has no malware, making it the preferred OS for backend JavaEE developers who need a reliable server environment.

Installation

Linux can be installed directly on a physical PC or inside a virtual machine. Common VM software includes VMWare (paid, trial available) and VirtualBox (free, originally from Sun, now Oracle).

Connecting from Windows to a Linux VM

Use ifconfig or ip addr inside Linux to view IP information, then from Windows run ping www.mobaijun.com to test connectivity.

Client Tools for Remote Access

Popular SSH/Telnet clients are SecureCRT/SecureFX and XShell/XFtp.

Linux Directory Structure

All paths start at the root /. Key directories:

bin : system commands

root : root user’s home

home : regular users’ homes

usr : shared resources, typical install location /usr/local etc : configuration files (e.g., network, permissions)

Directory Operations

Change directory: / – root . – current .. – parent ~ – current user’s home - – previous directory

Create directories: mkdir directory_name Create nested directories: mkdir -p /parent/child List files: ls -l – detailed list ls -a – include hidden files

Search files: find [path] -name "pattern" Rename/Move:

mv old_name new_name   # rename

mv source_dir target_dir   # move

Copy: cp -r source target # recursive copy Delete:

rm -r directory   # recursive delete

rm -f file   # force delete

-p creates missing parent directories automatically.

Viewing File Contents

cat filename

– full content more filename – paged view head filename – first 10 lines head -n 20 filename – first 20 lines tail filename – last 10 lines tail -n 20 filename – last 20 lines less filename – full view with line numbers, navigation, quit with

q

Editing Files with vi/vim

Command mode: i – insert before cursor a – insert after cursor o – open new line below

Common editing commands: yy – yank (copy) current line p – paste after cursor dd – delete current line u – undo /pattern – search forward ( n), backward ( N) wp – write and quit q! – quit without saving

Compression and Extraction

Supported extensions: .zip/.rar – Windows archives .tar – Linux tarball .gz – gzip .tar.gz – tarball compressed with gzip

Create archive: tar -cvzf archive_name.tar.gz file1 file2 ... Extract archive:

tar -xvzf archive_name.tar.gz -C /target/directory

Process and Memory Management

List processes:

ps -a   # all users

ps -u   # detailed info

ps -x   # all processes

Show memory usage: top Terminate process:

kill -9 PID   # force kill

Network Management

Hostname:

# view hostname
hostname
# set hostname permanently
hostnamectl set-hostname new_name

Network service control:

systemctl start network
systemctl stop network
systemctl restart network
systemctl status network

Static IP configuration (CentOS example): edit /etc/sysconfig/network-scripts/ifcfg-ens32 and set ONBOOT=no to disable, ONBOOT=yes to enable, then restart network.

Check ports and listening sockets:

netstat -nutlp

Firewall Management (firewalld)

systemctl status firewalld

– view status systemctl start firewalld – enable systemctl stop firewalld – disable systemctl enable firewalld – start on boot systemctl disable firewalld – prevent auto‑start

SSH Key‑Based Login

# generate key pair
ssh-keygen
# copy public key to remote host
ssh-copy-id user@host
# test password‑less login
ssh user@host

Package Management (RPM & YUM)

RPM common options: -v – verbose -q – query -a – list all packages -i – install --nodeps – ignore dependencies (used with -e to force uninstall)

Example queries:

rpm -qa               # list all installed packages
rpm -ivh package.rpm   # install
rpm -e --nodeps package.rpm   # force uninstall

Change YUM source (CentOS 7):

yum install -y wget
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
yum clean all
yum makecache
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
vim /etc/yum.repos.d/CentOS-Base.repo   # replace http with https
yum update

MySQL Installation and Remote Access

# check existing MySQL
rpm -qa | grep mysql
# download repo package
wget https://repo.mysql.com//mysql80-community-release-el7-1.noarch.rpm
rpm -ivh mysql80-community-release-el7-1.noarch.rpm
# install client, server, tools
yum -y install mysql-community-client mysql-community-server mysql-community-devel
# start and enable service
systemctl start mysqld
systemctl enable mysqld
# set root password
mysql -uroot -e "SET PASSWORD = PASSWORD('root');"
# enable remote login
mysql -uroot -proot -e "GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'root'; FLUSH PRIVILEGES;"
# open firewall port 3306
firewall-cmd --zone=public --add-port=3306/tcp --permanent
systemctl restart firewalld

Tomcat Deployment

# upload and extract
tar -xvf apache-tomcat-8.5.55-src.tar.gz -C /usr/local/
mv apache-tomcat-8.5.55-src tomcat8
cd /usr/local/apache-tomcat-8.5.55-src/bin
chmod u+x *.sh
./startup.sh   # start Tomcat
# open firewall for port 8080
firewall-cmd --zone=public --add-port=8080/tcp --permanent
systemctl restart firewalld
# if JAVA_HOME missing, edit setclasspath.sh
export JAVA_HOME=/usr/local/jdk1.8.0_251
export JRE_HOME=$JAVA_HOME/jre

Project Publishing

Import database, build a WAR in IDEA, copy the WAR to /usr/local/tomcat8/webapps, then restart Tomcat with shutdown.sh and startup.sh. Fix MySQL charset by adding ?characterEncoding=utf8 to the JDBC URL in druid.properties.

User and Group Management

# add user and home directory
useradd -m mobaijun
# set password
passwd mobaijun
# switch user
su mobaijun
# delete user and its group
userdel -r tom
# modify login name
usermod -l Rose mobaijun
# add group
groupadd dev
# add user to group
usermod -g dev mobaijun
# remove user from group
gpasswd -d mobaijun dev
# rename group
groupmod -n newdev dev
# delete group
groupdel newdev

Grant sudo privileges by editing /etc/sudoers and adding appropriate entries.

Scheduled Tasks (crontab)

crontab -l          # list current jobs
crontab -e          # edit jobs
crontab -r          # remove all jobs
* * * * * command  # run every minute

Additional Tools

Use netstat -nutlp to view listening ports, ssh-keygen for key generation, and ping to test connectivity.