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Mastering Containers, Filesystems & Storage in Linux

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Containers: Lightweight Application Virtualization

Core Concepts:

  • Virtualization Method: Isolates apps using namespaces (PID, network, mount) and cgroups (resource limits).
  • Containers vs. VMs:
    • VMs: Emulate full OS (heavy, hypervisor-dependent).
    • Containers: Share host kernel (lightweight, faster startup).
docker run -it ubuntu:22.04 /bin/bash  # Run container interactively

Docker Essentials:

  1. Installation:
    bash sudo apt install docker.io # Debian/Ubuntu sudo systemctl enable --now docker
  2. Key Commands:
    bash docker pull nginx:latest # Download image docker ps -a # List containers docker build -t myapp . # Build image from Dockerfile
  3. docker-compose: Orchestrate multi-container apps:
    yaml # docker-compose.yml services: web: image: nginx ports: - "80:80" bash docker-compose up -d # Launch stack

Linux Filesystems: Structure & Types

Organization & VFS:

  • Hierarchy: / (root) → /bin, /etc, /home, /var.
  • VFS Role: Unifies access to all filesystems (ext4, NFS, tmpfs) via standardized system calls.

Filesystem Types:

Type Use Case Journaling
ext4 General-purpose Yes
XFS Large files Yes
Btrfs Snapshots, RAID Yes
tmpfs RAM-backed temp No
NFS Network shares Depends

Why Journaling? Prevents corruption after crashes by logging changes first.

Disk Management & Partitioning

Hardware & Naming:

  • Disk Types: HDD (spinning platters), SSD (flash), NVMe (PCIe-attached).
  • Device Nodes:
    • /dev/sda: First SATA disk
    • /dev/nvme0n1: First NVMe disk
    • /dev/sda1: First partition on SATA disk

Partitioning Tools:

sudo fdisk /dev/sdb            # Interactive partitioning 
sudo blkid                     # Show UUIDs/filesystems 
lsblk -o NAME,SIZE,FSTYPE,MOUNTPOINT  # Tree view

Strategies & Backup:

  • MBR vs. GPT: GPT supports >2TB disks and >4 partitions.
  • Backup Partition Table:
    bash sudo sfdisk -d /dev/sda > sda-backup.txt # Backup sudo sfdisk /dev/sda < sda-backup.txt # Restore

Filesystem Operations

Creation & Maintenance:

sudo mkfs.ext4 /dev/sdb1       # Format partition 
sudo fsck /dev/sdb1            # Check/repair errors 
sudo chattr +i /critical/file  # Immutable file (ext4) 
lsattr /secret/config          # View extended attributes

Mounting & Automation:

  • Manual Mount:
    bash sudo mount /dev/sdb1 /mnt/data
  • Permanent Mount: Add to /etc/fstab:
    UUID=abcd1234 /mnt/data ext4 defaults 0 2
  • Network Filesystems:
    bash sudo mount -t nfs 192.168.1.10:/share /mnt/nfs
  • Automount (autofs): Mount on-demand when accessed.

ext4 Deep Dive

Structure:

  • Superblock: Filesystem metadata (size, block count).
  • Inodes: Store file attributes (permissions, timestamps).
  • Block Groups: Divide disk for parallel access.

Utilities:

sudo dumpe2fs /dev/sda1        # Show ext4 details 
sudo tune2fs -c 30 /dev/sda1   # Check every 30 mounts

LVM: Flexible Storage Management

Concepts:

  • Physical Volume (PV): Disk/partition (/dev/sdb).
  • Volume Group (VG): Pool of PVs.
  • Logical Volume (LV): Virtual partition created from VG.

Operations:

# Create LV 
sudo pvcreate /dev/sdb                # Mark disk as PV 
sudo vgcreate myvg /dev/sdb           # Create VG 
sudo lvcreate -L 20G -n mylv myvg     # Create 20G LV 
sudo mkfs.ext4 /dev/myvg/mylv         # Format 

# Resize LV (extend) 
sudo lvextend -L +5G /dev/myvg/mylv   # Add 5G 
sudo resize2fs /dev/myvg/mylv          # Resize filesystem 

# Snapshots (point-in-time backup) 
sudo lvcreate -s -n snap -L 1G /dev/myvg/mylv

Troubleshooting Toolkit

Tool Purpose
df -h Disk space by filesystem
**du -sh *** Directory sizes
dmesg Kernel logs (disk errors)
lsblk Block device topology
iostat Disk I/O performance

Key Takeaways

  1. Containers isolate apps; Docker simplifies deployment.
  2. ext4/XFS handle journalling; tmpfs uses RAM.
  3. LVM enables dynamic storage: resize LVs, snapshot data.
  4. Always backup partition tables before modifying disks.
# Audit filesystem health: 
sudo fsck -AN; sudo dmesg | grep -i "error"; df -h

Next: Deep dive into Kubernetes orchestration!

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