Package Management with YUM

On RPM-based distributions like CentOS or RHEL, the yum package manager is the standard tool for software management.

Installing Software:

yum install package_name
# Example:
yum install htop

Removing Software:

yum remove package_name
# Example:
yum remove htop

Searching for Packages: Supports fuzzy matching to find relevant packages.

yum search keyword

Additional Operations:

# Clear cached package data
yum clean packages

# List all installed packages
yum list

# Display detailed information about a package
yum info package_name

System Resource Monitoring

Monitoring hardware resources is crucial for maintaining server health.

Memory Usage: Use the -h flag for human-readable output or -m for megabytes.

free -m

Disk Space: View file system disk space usage.

df -h

System Load: Check load averages and uptime. A load average consistently above 0.7 may indicate performance issues.

w
# or
top

CPU Information: Detailed processor specifications can be found in the proc filesystem.

cat /proc/cpuinfo

File Operations and Text Editing

Key directories include /home for user files, /etc for system configurations, and /tmp for temporary data.

Vim Editor Basics: Vim is a powerful modal text editor.

• Navigation: gg jumps to the first line; G jumps to the last line.
• Editing: dd deletes the current line; u undoes the last action.
• Clipboard: yy copies (yanks) a line; p pastes it.
• Search: In command mode, type /keyword and press Enter.
• Line Numbers: In command mode, type :set number to display line counts.

Content Search and Analysis:

# Search for 'error' in a file and show line numbers
grep -n 'error' server.log

# Count total lines in a file
cat server.log | wc -l

# Count occurrences of a specific pattern
grep -c '200 OK' server.log

File Searching: The find command locates files based on criteria.

# Find all C source files in the current directory
find . -name "*.c"

File Compression: The tar command is used for archiving.

# Create a gzip compressed archive
tar -czvf archive.tar.gz /path/to/directory

# List contents of an archive
tar -tzvf archive.tar.gz

# Extract an archive
tar -xzvf archive.tar.gz

User Management

Managing user accounts is a fundamental administrative task.

# Add a new user
useradd devuser

# Set or change the user's password
passwd devuser

# Remove a user and their home directory
userdel -r devuser

Firewall Configuration

The firewalld service manages network security.

Service Management:

# Check service status
ps -ef | grep firewalld

# Start, stop, or restart the service
systemctl start firewalld
systemctl stop firewalld
systemctl restart firewalld

Firewall-cmd Operations:

# Check runtime state
firewall-cmd --state

# List all open ports
firewall-cmd --list-ports

# Open a port permanently (requires reload)
firewall-cmd --add-port=8080/tcp --permanent
firewall-cmd --reload

# Allow a service
firewall-cmd --add-service=http

Privilege Escalation and File Transfer

Sudo Configuration: To grant a user administrative privileges, edit the sudoers file using visudo and add the user to the privilege specification section.

# Run as root
su -
visudo

# Add line:
devuser ALL=(ALL) ALL

File Download:

# Using wget
cd /tmp
wget http://example.com/file.zip

# Using curl
curl -O http://example.com/file.zip

Secure Copy (SCP):

# Upload local file to remote server
scp local_file.txt user@192.168.1.50:/tmp/

# Download remote file to local machine
scp user@192.168.1.50:/tmp/remote_file.txt ./

Terminal File Transfer (ZModem): Requires the lrzsz package.

# Install utility
yum install lrzsz

# Upload file (opens file dialog in secure CRT/Xshell)
rz

# Download file
sz file_name