Package Management

Here’s a clear and structured guide for Package Management and related Linux system topics:

---

📦 Linux Package Management & File System Structure

---

1. 📁 The Linux File System Structure (Simplified)

Directory	Purpose
/	Root of the file system.
/bin	Essential binary programs (e.g. ls, cp, bash).
/sbin	System binaries (e.g. reboot, mount).
/etc	Configuration files.
/dev	Device files.
/home	User directories.
/lib	Essential shared libraries.
/opt	Optional software.
/usr	User-installed software and libraries.
/var	Variable files (e.g., logs, spools).
/tmp	Temporary files.
/mnt, /media	Mount points for removable storage.

---

2. 📚 Managing Shared Libraries

Tool / File	Description
ldd binary	Lists shared libraries required by a binary.
ldconfig	Updates the dynamic linker runtime bindings.
/etc/ld.so.conf	File listing directories for shared libraries.
LD_LIBRARY_PATH	Temporary environment variable to specify additional library paths.

Example:

export LD_LIBRARY_PATH=/custom/lib:$LD_LIBRARY_PATH

---

3. 📦 Debian Package Management

a. /etc/apt/sources.list

Defines package sources:

deb http://deb.debian.org/debian stable main contrib non-free

b. apt-get – Basic commands:

sudo apt-get update        # Update package list
sudo apt-get upgrade       # Upgrade installed packages
sudo apt-get install pkg   # Install a package
sudo apt-get remove pkg    # Remove a package

c. dpkg

Low-level package tool:

sudo dpkg -i package.deb    # Install .deb file
sudo dpkg -r package         # Remove package
dpkg -l | grep pkgname       # List package info

d. apt-cache

Query APT package cache:

apt-cache search firefox
apt-cache show firefox

e. aptitude (TUI tool, optional)

sudo aptitude        # Launch UI
sudo aptitude install pkgname

---

4. 📦 RPM and YUM Package Management

f. /etc/yum.conf and /etc/yum.repos.d/

• yum.conf: Main configuration.
• .repo files in /etc/yum.repos.d/ define repository sources.

g. yumdownloader

Download RPMs without installing:

sudo yum install yum-utils
yumdownloader package

h. rpm and rpm2cpio

• Install:

sudo rpm -ivh package.rpm

• Convert .rpm to .cpio archive:

rpm2cpio file.rpm | cpio -idmv

---

5. 🔗 Creating Symbolic and Hard Links

Link Type	Command	Description
Symbolic (soft) link	ln -s target linkname	Points to a file or directory path.
Hard link	ln target linkname	Points to same inode; works only within same filesystem.

Examples:

ln -s /etc/nginx/nginx.conf ~/nginx.conf_link
ln /bin/ls ~/ls_hardlink

---