Data rotation and cleanup in Raspberry Pi - Step-by-Step Execution

Concept Flow - Data rotation and cleanup

Start

↓

Check data size or age

↓

Is data too old or large?

No→Wait or Exit

Yes↓

Rotate data: archive or move old data

↓

Cleanup: delete or compress old files

↓

Log actions

↓

End or repeat

This flow checks if data is too old or large, then rotates and cleans it up to save space and keep things organized.

Execution Sample

Raspberry Pi

import os
import time

if os.path.getsize('log.txt') > 1000:
    os.rename('log.txt', f'log_{int(time.time())}.txt')
    open('log.txt', 'w').close()

This code checks if 'log.txt' is bigger than 1000 bytes, renames it with a timestamp, and creates a new empty 'log.txt'.

Execution Table

Step	Action	Condition	Result	Output
1	Check size of 'log.txt'	Size > 1000?	True	Size is 1500 bytes
2	Rename 'log.txt' to 'log_<timestamp>.txt'	N/A	File renamed	log_1687000000.txt
3	Create new empty 'log.txt'	N/A	File created empty	log.txt size 0 bytes
4	End process	N/A	Cleanup done	Ready for new logs

💡 Data rotated because size exceeded 1000 bytes

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
log.txt size (bytes)	1500	1500	N/A (renamed)	0	0
log file name	'log.txt'	'log.txt'	'log_<timestamp>.txt'	'log.txt'	'log.txt'

Key Moments - 2 Insights

Why do we rename the file before creating a new one?

Renaming preserves the old data by moving it to a new file, so we don't lose logs before starting fresh, as shown in step 2 of the execution table.

What happens if the file size is not greater than 1000?

The code skips renaming and cleanup, so the file stays the same. This is implied by the condition in step 1.

Visual Quiz - 3 Questions

Look at the execution table, what is the size of 'log.txt' after step 3?

A 1500 bytes

B 1000 bytes

C 0 bytes

D File deleted

💡 Hint

Check the 'Result' and 'Output' columns in step 3 of the execution table.

At which step is the old log file renamed?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column to find when renaming happens.

If the file size was 900 bytes, what would happen?

A No action taken

B New empty file created

C File would be renamed

D File deleted

💡 Hint

Refer to the condition in step 1 about size > 1000.

Concept Snapshot

Data rotation and cleanup:
- Check data size or age
- If too large/old, rename or archive data
- Create new empty file or compress old data
- Helps keep storage clean and organized
- Common in log file management on Raspberry Pi

Full Transcript

This example shows how to manage data files on a Raspberry Pi by checking if a file is too large, then renaming it with a timestamp to save old data, and creating a new empty file for fresh data. This process is called data rotation and cleanup. It helps keep storage organized and prevents files from growing too big. The code checks the file size, renames the file if needed, and resets the original file. The execution table traces each step, showing variable changes and actions. This method is useful for managing logs or data files that grow over time.

Practice

1. What is the main purpose of data rotation and cleanup on a Raspberry Pi?

easy

A. To keep storage organized and remove old files

B. To increase the CPU speed

C. To install new software automatically

D. To change the screen resolution

Solution

1. Step 1: Understand data rotation and cleanup

   Data rotation and cleanup help manage files by removing old or unnecessary data.

2. Step 2: Identify the main goal

   The goal is to keep storage organized and free space by deleting old files.

3. Final Answer:

   To keep storage organized and remove old files -> Option A

4. Quick Check:

   Data rotation = storage cleanup [OK]

Hint: Think about storage space and file management [OK]

Common Mistakes:

• Confusing data cleanup with hardware upgrades
• Thinking it changes system performance directly
• Assuming it installs software automatically

2. Which of the following commands correctly deletes files older than 7 days in the /var/log directory on Raspberry Pi?

easy

A. find /var/log -type d -mtime +7 -delete

B. find /var/log -type f -mtime +7 -delete

C. rm /var/log/* -mtime +7

D. delete /var/log -older 7

Solution

1. Step 1: Understand the find command syntax

   To delete files older than 7 days, use find with -type f (files), -mtime +7 (older than 7 days), and -delete.

2. Step 2: Check each option

   find /var/log -type f -mtime +7 -delete uses correct syntax. find /var/log -type d -mtime +7 -delete targets directories (-type d), not files. rm /var/log/* -mtime +7 uses rm incorrectly with -mtime. delete /var/log -older 7 is not a valid command.

3. Final Answer:

   find /var/log -type f -mtime +7 -delete -> Option B

4. Quick Check:

   find + -mtime +7 + -delete = correct [OK]

Hint: Use find with -type f and -mtime +days to delete old files [OK]

Common Mistakes:

• Using -type d instead of -type f
• Trying to use rm with -mtime option
• Using invalid commands like delete

3. What will be the output of this script snippet on Raspberry Pi?

logfile="/var/log/syslog"
backup="/var/log/syslog-$(date +%Y%m%d)"

mv $logfile $backup
> $logfile
ls /var/log/syslog*

medium

A. Only /var/log/syslog-YYYYMMDD file listed

B. Only /var/log/syslog file listed

C. /var/log/syslog and /var/log/syslog-YYYYMMDD files listed

D. No files listed, error occurs

Solution

1. Step 1: Understand the script actions

   The script renames syslog to syslog-YYYYMMDD (today's date), then creates a new empty syslog file.

2. Step 2: Predict the ls output

   After these steps, both /var/log/syslog (empty) and /var/log/syslog-YYYYMMDD exist, so ls lists both.

3. Final Answer:

   /var/log/syslog and /var/log/syslog-YYYYMMDD files listed -> Option C

4. Quick Check:

   mv + new empty file + ls = both files [OK]

Hint: Renaming then recreating file shows both in listing [OK]

Common Mistakes:

• Thinking syslog file is deleted
• Assuming mv copies instead of moves
• Ignoring the empty file creation with >

4. Identify the error in this Raspberry Pi log rotation script snippet:

logfile="/var/log/app.log"
backup="/var/log/app.log-$(date +%Y%m%d)"

mv $logfile $backup
> $logfile
find /var/log -type f -mtime 7 -delete

medium

A. The find command should use -mtime +7 to delete files older than 7 days

B. The mv command syntax is incorrect

C. The > $logfile line should be before mv command

D. The backup filename format is invalid

Solution

1. Step 1: Check the find command usage

   The find command uses -mtime 7 which matches files exactly 7 days old, not older than 7 days.

2. Step 2: Correct the find command

   To delete files older than 7 days, use -mtime +7 instead of -mtime 7.

3. Final Answer:

   The find command should use -mtime +7 to delete files older than 7 days -> Option A

4. Quick Check:

   find -mtime +7 deletes older files [OK]

Hint: Use + before days in -mtime to delete older files [OK]

Common Mistakes:

• Using -mtime 7 deletes only files exactly 7 days old
• Misplacing the > $logfile line
• Incorrect mv command syntax

5. You want to automate log rotation on your Raspberry Pi so that every day the current log file /var/log/myapp.log is renamed with the date, a new empty log is created, and logs older than 14 days are deleted. Which script snippet correctly performs this task?

hard

A. mv /var/log/myapp.log /var/log/myapp.log-$(date +%Y%m%d)
> /var/log/myapp.log
find /var/log -type f -name 'myapp.log-*' -mtime 14 -delete

B. mv /var/log/myapp.log /var/log/myapp.log-$(date +%Y%m%d)
rm /var/log/myapp.log
find /var/log -type f -mtime +14 -delete

C. backup="/var/log/myapp.log-$(date +%Y%m%d)"
cp /var/log/myapp.log $backup
> /var/log/myapp.log
find /var/log -type f -name 'myapp.log-*' -mtime 14 -delete

D. backup="/var/log/myapp.log-$(date +%Y%m%d)"
mv /var/log/myapp.log $backup
> /var/log/myapp.log
find /var/log -type f -name 'myapp.log-*' -mtime +14 -delete

Solution

1. Step 1: Rename current log and create new empty log

   backup="/var/log/myapp.log-$(date +%Y%m%d)" mv /var/log/myapp.log $backup > /var/log/myapp.log find /var/log -type f -name 'myapp.log-*' -mtime +14 -delete correctly moves the log file to a dated backup and creates a new empty log with >.

2. Step 2: Delete logs older than 14 days

   backup="/var/log/myapp.log-$(date +%Y%m%d)" mv /var/log/myapp.log $backup > /var/log/myapp.log find /var/log -type f -name 'myapp.log-*' -mtime +14 -delete uses find with -name 'myapp.log-*' and -mtime +14 to delete backups older than 14 days, which is correct.

3. Final Answer:

   backup="/var/log/myapp.log-$(date +%Y%m%d)" mv /var/log/myapp.log $backup > /var/log/myapp.log find /var/log -type f -name 'myapp.log-*' -mtime +14 -delete -> Option D

4. Quick Check:

   mv + new file + find -mtime +14 = correct rotation [OK]

Hint: Move log, recreate empty, delete backups older than 14 days [OK]

Common Mistakes:

• Using rm instead of recreating empty log
• Using -mtime 14 instead of +14 in find
• Copying instead of moving log file