Linux Package Management: Day 05

📦 What is Package Management?

Linux uses package managers to install, update, and remove software efficiently while resolving dependencies.

🧰 1. Debian/Ubuntu: apt (Advanced Package Tool)

Update package list:

sudo apt update

Upgrade packages:

sudo apt upgrade

Install a package:

sudo apt install package-name

Remove a package:

sudo apt remove package-name

Remove unused packages:

sudo apt autoremove

Search for a package:

apt search nginx

🍱 2. RHEL/CentOS/Rocky: yum and dnf

On RHEL 8+ and Fedora, use dnf instead of yum.

Update repository cache:

sudo dnf makecache

Install a package:

sudo dnf install httpd

Remove a package:

sudo dnf remove httpd

List installed packages:

dnf list installed

Search packages:

dnf search nginx

📁 3. Using rpm Directly

Install from .rpm file:

sudo rpm -ivh package.rpm

Upgrade an RPM:

sudo rpm -Uvh package.rpm

Remove an RPM:

sudo rpm -e package-name

Query installed RPMs:

rpm -qa | grep nginx

🧊 4. openSUSE: zypper

Install a package:

sudo zypper install vim

Remove a package:

sudo zypper remove vim

Update system:

sudo zypper update

Search:

zypper search nginx

📜 5. Package Information

Show detailed package info:

APT:

apt show curl

DNF:

dnf info curl

RPM:

rpm -qi curl

🗃️ 6. Cleaning Up

APT:

sudo apt clean
sudo apt autoremove

DNF/YUM:

sudo dnf clean all

🛡️ 7. GPG Keys and Repositories

Add a GPG key (APT):

wget -qO - https://example.com/key.gpg | sudo apt-key add -

Add a custom repo (YUM/DNF):

Create file in /etc/yum.repos.d/custom.repo:

[custom-repo]
name=Custom Repository
baseurl=http://example.com/repo/
enabled=1
gpgcheck=0

✅ Summary

Linux package management ensures reliable and secure software deployment.

🛠️ How to Create a Local YUM Repository Using an ISO

This guide explains how to set up a local YUM repository from an ISO file on RHEL, CentOS, AlmaLinux, or Rocky Linux.

📥 1. Mount the ISO File

mkdir -p /mnt/iso
mount -o loop /dev/sr0 /mnt/iso

📂 2. Copy ISO Contents (Optional but Recommended)

mkdir -p /var/www/html/yumrepo
cp -av /mnt/iso/* /var/www/html/yumrepo/
umount /mnt/iso

This step ensures the repository is persistent across reboots.

📝 3. Create the Local Repo File

Create a new file /etc/yum.repos.d/local.repo with the following content:

✅ If you copied the ISO contents:

[LocalRepo]
name=Local Repository
baseurl=file:///var/www/html/yumrepo
enabled=1
gpgcheck=0

🔁 If using the ISO directly (without copying):

[LocalRepo]
name=Local Repository
baseurl=file:///mnt/iso
enabled=1
gpgcheck=0

• Example is given below:

🔄 4. Clean YUM and Check the Repository

yum clean all
yum repolist

You should now see LocalRepo listed in the repository list.

🌐 5. (Optional) Serve the Repo via HTTP

This is useful if you want to share the repo with other machines.

Install Apache:

yum install -y httpd
systemctl enable --now httpd

Allow Apache Access with SELinux (if enabled):

chcon -R -t httpd_sys_content_t /var/www/html/yumrepo

Update the Repo File:

Edit /etc/yum.repos.d/local.repo to use HTTP:

[LocalRepo]
name=Local Repository
baseurl=http://localhost/yumrepo
enabled=1
gpgcheck=0

✅ Done!

You now have a local YUM repository set up using an ISO image. You can use it offline, or serve it to multiple machines via HTTP.

📊 Linux Monitoring

Monitoring Linux is critical for performance tuning, capacity planning, and troubleshooting. Below are essential CLI tools for real-time and historical system monitoring.

🧠 1. CPU and Memory Monitoring

top — real-time system performance

top

• Press M to sort by memory.
• Press P to sort by CPU usage.

htop — enhanced top (colorful UI)

htop

Install via: sudo apt install htop or sudo dnf install htop

vmstat — memory, processes, and system info

vmstat 1 5

• 1 5: sample every second for 5 times

free — memory usage

free -h

💿 2. Disk Monitoring

df — disk space usage

df -h

du — directory size

du -sh /var/log

iostat — CPU and I/O stats

iostat -xz 1 3

Install via: sudo apt install sysstat or sudo dnf install sysstat

🌐 3. Network Monitoring

ip a or ifconfig — IP addresses

ip a

ss — socket statistics (replacement for netstat)

ss -tuln

• -tuln: TCP/UDP listening sockets without resolving names

netstat — old but useful

netstat -plntu

Might require net-tools package.

nload — network bandwidth usage

nload

Install: sudo apt install nload or sudo dnf install nload

📈 4. System Activity Reports

sar — historical performance stats

sar -u 1 3

Collects CPU usage every 1 second, 3 times.

Enable sar:

sudo systemctl enable sysstat
sudo systemctl start sysstat

🔍 5. Process & Service Monitoring

ps — process status

ps aux | grep nginx

pidstat — individual process usage

pidstat -p <PID>

systemctl — service status

systemctl status nginx

🧪 6. Other Useful Tools

✅ Summary Table

🔁 Automating Monitoring Reports

You can use cron to schedule logs and save stats:

*/5 * * * * sar -u 1 5 >> /var/log/cpu_usage.log

Linux monitoring is essential to keep your systems healthy and responsive. Regular usage of these tools helps you stay ahead of issues before they impact users.