Backup strategies in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a full backup?

A full backup copies all selected files and data every time it runs. It is simple but can take more time and space.

beginner

Explain incremental backup.

An incremental backup saves only the changes made since the last backup, making it faster and smaller but requires all previous backups to restore.

intermediate

What is the difference between differential and incremental backups?

Differential backups save changes since the last full backup, while incremental backups save changes since the last backup of any type. Differential grows larger over time; incremental stays small.

beginner

Why is it important to test your backups?

Testing backups ensures data can be restored correctly. Without testing, backups might be corrupted or incomplete, risking data loss.

beginner

What is the 3-2-1 backup rule?

Keep 3 copies of your data, on 2 different types of storage, with 1 copy offsite. This protects against hardware failure, theft, or disasters.

Which backup type saves only files changed since the last backup of any kind?

A Incremental backup

B Full backup

C Differential backup

D Mirror backup

Incremental backups save only changes since the last backup, making them efficient in time and space.

What does the '1' represent in the 3-2-1 backup rule?

A One backup copy stored on the same device

B One backup copy stored locally

C One backup copy stored offsite

D One backup copy stored in the cloud only

The '1' means at least one backup copy should be stored offsite to protect against local disasters.

Which backup type requires all previous backups to restore data?

A Snapshot backup

B Full backup

C Differential backup

D Incremental backup

Incremental backups depend on all previous backups to restore the full data set.

Why might differential backups grow larger over time?

A They save changes since the last full backup

B They save changes since the last incremental backup

C They save all files every time

D They compress data more

Differential backups accumulate all changes since the last full backup, so size grows until next full backup.

What is a key reason to automate backups in Linux CLI?

A To avoid using disk space

B To ensure backups run regularly without manual effort

C To delete old backups automatically

D To speed up the computer

Automation ensures backups happen on schedule, reducing risk of forgetting or human error.

Describe the main types of backup strategies and when you might use each.

Think about how much data changes and how fast you want backups.

Explain the 3-2-1 backup rule and why it is important for data safety.

Consider risks like hardware failure and disasters.

Practice

1. Which of the following best describes the main purpose of a backup in Linux?

easy

A. To delete old files to free up space

B. To install new software updates automatically

C. To speed up the computer by cleaning temporary files

D. To save copies of important files in a safe place

Solution

1. Step 1: Understand what a backup is

   A backup is a copy of important data saved separately to protect against loss.

2. Step 2: Match the description to the options

   Only To save copies of important files in a safe place describes saving copies in a safe place, which is the purpose of backups.

3. Final Answer:

   To save copies of important files in a safe place -> Option D

4. Quick Check:

   Backup = Save copies safely [OK]

Hint: Backups always mean saving copies, not deleting files [OK]

Common Mistakes:

• Confusing backup with deleting files
• Thinking backup speeds up the system
• Mixing backup with software updates

2. Which command syntax correctly copies a directory and its contents to a backup folder?

easy

A. cp -r /home/user/docs /backup/docs

B. cp /home/user/docs /backup/docs

C. cp -d /home/user/docs /backup/docs

D. cp -x /home/user/docs /backup/docs

Solution

1. Step 1: Identify the correct option to copy directories recursively

   The -r option in cp copies directories and their contents recursively.

2. Step 2: Check other options for correctness

   The plain cp lacks -r, so it won't copy directories properly. The options with -d and -x use invalid or unrelated flags.

3. Final Answer:

   cp -r /home/user/docs /backup/docs -> Option A

4. Quick Check:

   Copy directory = cp -r [OK]

Hint: Use cp -r to copy folders with all files inside [OK]

Common Mistakes:

• Forgetting the -r flag for directories
• Using wrong flags like -d or -x
• Assuming cp copies folders without options

3. What will be the output of this command if the source directory has files and the destination is empty?

rsync -av /home/user/data/ /backup/data/

medium

A. Only lists files without copying them

B. Copies all files and folders from /home/user/data to /backup/data preserving attributes

C. Deletes all files in /backup/data and leaves it empty

D. Shows an error because /backup/data does not exist

Solution

1. Step 1: Understand rsync options -a and -v

   The -a option means archive mode (copy recursively and preserve attributes), and -v means verbose (show progress).

2. Step 2: Analyze command behavior

   Since /backup/data exists and is empty, rsync copies all files and folders from source to destination preserving attributes.

3. Final Answer:

   Copies all files and folders from /home/user/data to /backup/data preserving attributes -> Option B

4. Quick Check:

   rsync -av copies files with details [OK]

Hint: rsync -av copies and shows details, no deletion by default [OK]

Common Mistakes:

• Thinking rsync deletes files by default
• Confusing verbose with dry-run
• Assuming error if destination exists

4. You wrote this script to backup a folder:

#!/bin/bash
cp -r /home/user/docs /backup/docs
rm -r /home/user/docs/*

What is the main problem with this backup strategy?

medium

A. It deletes original files after copying, risking data loss

B. It does not copy hidden files

C. It uses the wrong command to copy files

D. It will fail because /backup/docs does not exist

Solution

1. Step 1: Analyze the script commands

   The script copies /home/user/docs to /backup/docs, then deletes all files inside /home/user/docs.

2. Step 2: Identify risk in deleting original files

   Deleting original files after copying is risky if the copy failed or is incomplete, causing data loss.

3. Final Answer:

   It deletes original files after copying, risking data loss -> Option A

4. Quick Check:

   Deleting originals after backup = risk [OK]

Hint: Never delete originals immediately after backup without verification [OK]

Common Mistakes:

• Assuming cp misses hidden files (it copies them)
• Thinking /backup/docs must exist (cp creates it)
• Ignoring risk of deleting original data

5. You want to automate daily backups of /home/user/projects to /mnt/backup using tar. Which command correctly creates a compressed backup file with the current date in its name?

hard

A. tar -czf /home/user/projects /mnt/backup/projects-$(date +%F).tar.gz

B. tar -cf /mnt/backup/projects.tar.gz /home/user/projects

C. tar -czf /mnt/backup/projects-$(date +%F).tar.gz /home/user/projects

D. tar -xzf /mnt/backup/projects-$(date +%F).tar.gz /home/user/projects

Solution

1. Step 1: Understand tar options for creating compressed archives

   -c creates an archive, -z compresses with gzip, and -f specifies the output file.

2. Step 2: Check command correctness

   tar -czf /mnt/backup/projects-$(date +%F).tar.gz /home/user/projects correctly creates a gzip compressed archive named with the current date in /mnt/backup from /home/user/projects.

3. Final Answer:

   tar -czf /mnt/backup/projects-$(date +%F).tar.gz /home/user/projects -> Option C

4. Quick Check:

   tar -czf + date = compressed dated backup [OK]

Hint: Use tar -czf with $(date +%F) for dated compressed backups [OK]

Common Mistakes:

• Using -xzf which extracts instead of creates
• Swapping source and destination paths
• Omitting compression flag -z