Unit 3: Managing Software and Storage

Section 1: Software Management

1.1 Understand Software Management

Modern Linux distributions use Package Management Systems to handle software installation, removal, and updates. Unlike manual installation, package managers handle:

• Dependencies: Automatically installing libraries required by the main program.
• Integrity: Verifying digital signatures to ensure software hasn't been tampered with.
• Version Control: managing updates and allowing rollbacks.
• Centralization: Pulling software from trusted repositories.

1.2 Manage RPM Software Packages and Repositories

Used by Red Hat Enterprise Linux (RHEL), CentOS, Fedora, and SUSE.

The RPM Database:
Stores information about installed packages. Located at /var/lib/rpm.

Low-Level Tool: rpm
Does not resolve dependencies. Useful for querying or installing specific standalone .rpm files.

• Install: rpm -ivh package_name.rpm (i=install, v=verbose, h=hash marks).
• Upgrade: rpm -Uvh package_name.rpm (Installs if not present, upgrades if present).
• Query: rpm -qa (Query All installed), rpm -qi package_name (Info).
• Remove: rpm -e package_name.
• Verify: rpm -V package_name (Checks if files have changed since installation).

High-Level Tools: yum and dnf
dnf is the successor to yum. Both resolve dependencies automatically by checking repositories.

• Repositories: Configured in /etc/yum.repos.d/*.repo.
• Install: dnf install package_name
• Update: dnf update (Updates all packages).
• Search: dnf search keyword.
• List: dnf list installed.
• Groups: dnf groupinstall "Development Tools".

1.3 Manage Debian-based Software Packages and Repositories

Used by Debian, Ubuntu, Linux Mint, and Kali.

Low-Level Tool: dpkg
Similar to rpm, it manages local .deb files but does not resolve dependencies.

• Install: dpkg -i package_name.deb
• Remove: dpkg -r package_name (keeps config files) or dpkg -P package_name (Purge; removes config).
• Status: dpkg -l (List all).
• Reconfigure: dpkg-reconfigure package_name.

High-Level Tools: apt (and apt-get)
Retrieves packages from repositories defined in /etc/apt/sources.list and /etc/apt/sources.list.d/.

• Update Index: apt update (Crucial first step: refreshes the local list of available package versions).
• Upgrade System: apt upgrade (Installs newer versions of installed packages).
• Install: apt install package_name.
• Remove: apt remove package_name.
• Search: apt search keyword.

1.4 Compile from Source Code

When software is not in a repository, or specific compile-time options are needed, admins must compile from source.

Prerequisites: Compiler (gcc), make, kernel headers (kernel-devel).

The Standard Workflow (The "Triad"):

1. Extract: Unpack the tarball.
   
   BASH

       tar -xzvf software-1.0.tar.gz
       cd software-1.0
       

2. Configure: Checks system for dependencies and creates a Makefile.
   
   BASH

       ./configure
       

3. Make: Compiles the source code into binary executables using the instructions in the Makefile.
   
   BASH

       make
       

4. Install: Copies the binaries to system directories (usually /usr/local/bin). Requires root.
   
   BASH

       sudo make install
       

1.5 Acquire Software

Before management, software must be retrieved.

• wget: Non-interactive network downloader. Good for unstable connections (can resume).
  • wget -c http://example.com/file.iso (Continue download).
• curl: Tool to transfer data to/from a server. Supports many protocols (HTTP, FTP, SCP).
  • curl -O http://example.com/file.zip (Save with original filename).
• git: Cloning source code repositories.
  • git clone https://github.com/user/project.git.

1.6 Run Software in a Sandbox

Sandboxing isolates applications from the core operating system to improve security and stability.

• Universal Packages (Snap & Flatpak):
  • Packages include their own dependencies (libraries), decoupling them from the OS version.
  • Snap: Developed by Canonical. snap install vlc.
  • Flatpak: Decentralized. flatpak install flathub org.gimp.GIMP.
• Containers (Docker/Podman):
  • Lightweight virtualization at the OS level.
  • Processes run in isolated namespaces (PID, Network, Mount).

Section 2: Storage Management

2.1 Understand Storage

Linux treats all storage devices as files under the /dev directory.

• Block Devices: Devices that move data in blocks (e.g., Hard Drives, SSDs, USBs).
  • IDE drives: /dev/hda
  • SATA/SCSI/USB drives: /dev/sda, /dev/sdb
  • NVMe drives: /dev/nvme0n1
• Partitions: Logical divisions of a physical disk.
  • /dev/sda1 (First partition on first disk).
• Partition Schemes:
  • MBR (Master Boot Record): Legacy, max 2TB drive, max 4 primary partitions.
  • GPT (GUID Partition Table): Modern (UEFI), huge size limits, 128+ partitions.

2.2 Deploy Storage

The process of making raw disk space available to the OS involves four steps:

1. Partitioning: Creating boundaries on the disk.
   • fdisk: Interactive tool for MBR (and GPT).
   • gdisk: Interactive tool for GPT.
   • parted: Command line tool for both.
2. Formatting (Creating Filesystem): Organizing the partition to store files.
   • mkfs.ext4 /dev/sdb1: Standard Linux filesystem.
   • mkfs.xfs /dev/sdb1: High-performance, default in RHEL.
   • mkfs.vfat: Compatibility with Windows/EFI.
3. Mounting: Attaching the filesystem to the directory tree.
   • mount /dev/sdb1 /mnt/data
4. Persistence: Ensuring mount survives reboot (/etc/fstab).
   • Format: UUID=... /mnt/data ext4 defaults 0 2

2.3 Manage Other Storage Options (LVM)

Logical Volume Management (LVM) allows for flexible resizing of storage spanning multiple physical disks.

LVM Architecture:

1. Physical Volume (PV): The raw disk or partition (pvcreate /dev/sdb).
2. Volume Group (VG): A pool of storage created by combining PVs (vgcreate my_vg /dev/sdb).
3. Logical Volume (LV): Carved out of the VG; acts like a partition (lvcreate -L 10G -n my_lv my_vg).
4. Filesystem: Placed on top of the LV (mkfs.xfs /dev/my_vg/my_lv).

Benefits:

• Live resizing (grow filesystems while online).
• Snapshots (for backups).
• Spanning filesystems across multiple physical drives.

2.4 Troubleshoot Storage

1. Disk Space Issues

• Symptom: "No space left on device" error.
• Check: df -h (Disk Free - human readable). Checks total capacity.
• Investigate: du -sh /var/* (Disk Usage). Checks which directory is consuming space.

2. Inode Exhaustion

• Symptom: Disk has free space (via df -h), but system says "No space left" or cannot create files.
• Cause: Too many small files used up all inodes (file index pointers).
• Check: df -i.
• Fix: Delete unnecessary small files or reformat with a higher inode count.

3. Filesystem Corruption

• Symptom: Read-only filesystem, I/O errors.
• Tool: fsck (File System Consistency Check).
  • Warning: Unmount the filesystem before running fsck.
  • Command: umount /dev/sdb1 followed by fsck -y /dev/sdb1.

4. Mount Issues

• Symptom: Boot failure (Emergency Mode).
• Cause: Errors in /etc/fstab (wrong UUID or syntax).
• Fix: Boot into maintenance mode, remount root read-write (mount -o remount,rw /), and edit /etc/fstab.