Overview
Checking disk space usage in Unix is a fundamental task for system administration, allowing the monitoring of available disk space and managing resources efficiently. This knowledge is crucial for maintaining system performance, preventing disk space exhaustion, and ensuring applications run smoothly.
Key Concepts
- df (disk free) command: Used to display the amount of available disk space for file systems.
- du (disk usage) command: Shows the disk space used by files and directories.
- File system hierarchy and management: Understanding how disk space is allocated and managed within Unix's file system hierarchy.
Common Interview Questions
Basic Level
- What is the command to check the disk space usage on a Unix system?
- How can you display the disk usage of a specific directory?
Intermediate Level
- How do you display the disk space usage of all files and directories in human-readable form?
Advanced Level
- Discuss how to monitor disk space usage in real-time or through scheduled checks.
Detailed Answers
1. What is the command to check the disk space usage on a Unix system?
Answer: The df command is used to check the disk space usage on a Unix system. It provides information about the total space and the available space on all mounted filesystems.
Key Points:
- df reports the amount of disk space used and available on filesystems.
- It can display the information in a human-readable format using the -h option.
- Understanding the output of df is crucial for managing disk space effectively.
Example:
# Display disk space usage for all filesystems
df
# Display disk space usage in a human-readable format
df -h
2. How can you display the disk usage of a specific directory?
Answer: To display the disk usage of a specific directory, you can use the du command. This command provides the amount of disk space used by files and directories.
Key Points:
- du is useful for identifying directories and files consuming significant disk space.
- It supports various options to customize the output, including -sh for showing total size in a human-readable format.
- This command helps in managing disk space by identifying large files/directories for potential cleanup.
Example:
# Display the disk usage of the current directory
du
# Display the total disk usage of a specific directory in a human-readable format
du -sh /path/to/directory
3. How do you display the disk space usage of all files and directories in human-readable form?
Answer: To display the disk space usage of all files and directories in a human-readable form, combine the du command with the -h option. Additionally, using -a displays all files, not just directories.
Key Points:
- The -h option makes the size output understandable (e.g., K for Kilobytes, M for Megabytes).
- The -a option includes all files in the output, not just the directories' sizes.
- This combination is powerful for detailed disk usage analysis.
Example:
# Display disk usage for all files and directories in human-readable form
du -ah /path/to/check
4. Discuss how to monitor disk space usage in real-time or through scheduled checks.
Answer: Monitoring disk space usage in real-time or through scheduled checks can be achieved by scripting with df and du, combined with watch for real-time monitoring or cron for scheduled checks.
Key Points:
- watch allows real-time monitoring by repeatedly executing commands at regular intervals.
- cron enables scheduling scripts or commands to run at specified times for regular disk usage checks.
- Combining these utilities with df and du provides a powerful toolset for disk space management.
Example:
# Real-time monitoring of disk space usage with watch
watch df -h
# Example cron job to check disk space usage daily and log to a file
# This cron job runs every day at midnight
0 0 * * * df -h > /path/to/log/disk_usage.log
By understanding and utilizing these commands and techniques, Unix system administrators can efficiently manage and monitor disk space usage, ensuring the system's health and performance.
