Log rotation script in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the log file exists.

Bash Scripting

if [ -f [1] ]; then
  echo "Log file found."
fi

Drag options to blanks, or click blank then click option'

A/home/user/data.txt

B/etc/passwd

C/var/log/syslog

D/tmp/tempfile

Attempts:

3 left

💡 Hint

Common Mistakes

Using a directory path instead of a file path.

Checking a file that does not exist on the system.

The -f option checks if the file exists and is a regular file. The log file is usually /var/log/syslog.

2fill in blank

medium

Complete the code to rename the current log file by adding a date suffix.

Bash Scripting

mv /var/log/syslog /var/log/syslog-[1]

Drag options to blanks, or click blank then click option'

A$(date +%Y%m%d)

B$(whoami)

C$(pwd)

D$(hostname)

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands that do not produce a date.

Forgetting the $ and parentheses around the command.

Using $(date +%Y%m%d) appends the current date in YYYYMMDD format to the log file name.

3fill in blank

hard

Fix the error in the code to compress the rotated log file using gzip.

Bash Scripting

gzip [1]

Drag options to blanks, or click blank then click option'

A/var/log/syslog-$(date +%Y%m%d)

B/var/log/syslog-$(date +%Y%m%d).gz

C/var/log/syslog

D/var/log/syslog-20230101

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to gzip the current log file which is still in use.

Trying to gzip a file that already has .gz extension.

You must gzip the actual rotated log file with the date suffix, not the current log or the compressed file.

4fill in blank

hard

Fill both blanks to create a function that rotates and compresses a log file.

Bash Scripting

rotate_log() {
  local logfile=[1]
  mv "$logfile" "$logfile-$(date +[2])"
  gzip "$logfile-$(date +[2])"
}

Drag options to blanks, or click blank then click option'

A/var/log/syslog

B%H%M%S

C%Y%m%d

D/var/log/auth.log

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect date format that does not match the gzip command.

Using a different log file path inconsistent with the rest of the script.

The function uses /var/log/syslog as the log file and %Y%m%d as the date format for the suffix.

5fill in blank

hard

Fill all three blanks to create a script that rotates, compresses, and deletes logs older than 7 days.

Bash Scripting

#!/bin/bash
logfile=[1]
rotate_date=$(date +[2])
mv "$logfile" "$logfile-$rotate_date"
gzip "$logfile-$rotate_date"
find /var/log -name "syslog-*" -mtime +[3] -delete

Drag options to blanks, or click blank then click option'

A/var/log/syslog

B%Y%m%d

C7

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong date format causing file name mismatches.

Deleting files older than wrong number of days.

The script uses /var/log/syslog as the log file, %Y%m%d for date format, and deletes logs older than 7 days.

Practice

1. What is the main purpose of a log rotation script in bash?

easy

A. To archive old log files and start new ones to prevent disk space issues

B. To delete all log files permanently

C. To create new log files without removing old ones

D. To convert log files into executable scripts

Solution

1. Step 1: Understand log rotation purpose

   Log rotation scripts archive old logs and create fresh logs to avoid disk space overflow.

2. Step 2: Compare options

   Only To archive old log files and start new ones to prevent disk space issues describes archiving old logs and starting new ones, which matches the purpose.

3. Final Answer:

   To archive old log files and start new ones to prevent disk space issues -> Option A

4. Quick Check:

   Log rotation = archive old + new logs [OK]

Hint: Log rotation means archiving old logs and starting fresh ones [OK]

Common Mistakes:

• Thinking log rotation deletes all logs
• Believing it only creates new logs without archiving
• Confusing log rotation with script conversion

2. Which of the following bash commands correctly appends the current date to a log filename for rotation?

easy

A. mv logfile.log logfile-date.log

B. mv logfile.log logfile-$(date +%Y-%m-%d).log

C. mv logfile.log logfile-$(date +%H:%M:%S).log

D. mv logfile.log logfile-$(date +%Y/%m/%d).log

Solution

1. Step 1: Understand date format for filenames

   Using $(date +%Y-%m-%d) produces a safe filename format like 2024-06-01.

2. Step 2: Check each option

   mv logfile.log logfile-$(date +%Y-%m-%d).log uses dashes which are safe in filenames. mv logfile.log logfile-date.log uses literal 'date', not dynamic. mv logfile.log logfile-$(date +%H:%M:%S).log uses colons which are invalid in filenames on many systems. mv logfile.log logfile-$(date +%Y/%m/%d).log uses slashes which are directory separators, invalid in filenames.

3. Final Answer:

   mv logfile.log logfile-$(date +%Y-%m-%d).log -> Option B

4. Quick Check:

   Date format with dashes = safe filename [OK]

Hint: Use date with dashes, avoid colons or slashes in filenames [OK]

Common Mistakes:

• Using colons or slashes in filenames
• Not using command substitution for date
• Using literal text instead of date command

3. Given this snippet in a log rotation script:

gzip logfile-$(date +%Y-%m-%d).log
ls logfile-*.log.gz | wc -l

What will the wc -l command output if there are 3 compressed log files matching the pattern?

medium

A. Error: No such file or directory

B. 0

C. 1

D. 3

Solution

1. Step 1: Understand the commands

   The gzip command compresses a log file, creating a file ending with .gz. The ls logfile-*.log.gz lists all compressed log files matching the pattern.

2. Step 2: Count matching files

   If there are 3 compressed log files, ls outputs 3 lines. Piping to wc -l counts these lines, so output is 3.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   Count of compressed logs = 3 [OK]

Hint: Count lines from ls output to get number of files [OK]

Common Mistakes:

• Assuming gzip outputs count
• Thinking wc -l counts characters
• Expecting error if files exist

4. Identify the error in this log rotation snippet:

mv logfile.log logfile-$(date +%Y-%m-%d).log
gzip logfile-$(date +%Y-%m-%d).log
rm logfile.log

medium

A. The date format uses slashes which are invalid

B. The gzip command is missing the -d option

C. The rm logfile.log command deletes the original log after moving, causing error

D. The mv command should use cp instead

Solution

1. Step 1: Analyze the commands order

   The mv command renames logfile.log to logfile-date.log, so logfile.log no longer exists after this.

2. Step 2: Check the rm command

   After moving, rm logfile.log tries to delete a file that was already moved, causing an error or no effect.

3. Final Answer:

   The rm logfile.log command deletes the original log after moving, causing error -> Option C

4. Quick Check:

   Deleting moved file causes error [OK]

Hint: Don't delete a file after moving it; it's already renamed [OK]

Common Mistakes:

• Deleting a file after moving it
• Confusing gzip options
• Using invalid date formats

5. You want to write a log rotation script that keeps only the last 5 compressed log backups and deletes older ones. Which bash command snippet correctly deletes older backups?

hard

A. ls -1t logfile-*.log.gz | tail -n +6 | xargs rm -f

B. ls -1t logfile-*.log.gz | head -n +6 | xargs rm -f

C. ls -1 logfile-*.log.gz | tail -n 5 | xargs rm -f

D. ls logfile-*.log.gz | grep -v 'logfile-*.log.gz' | xargs rm -f

Solution

1. Step 1: Understand the command parts

   ls -1t lists files sorted by modification time, newest first. tail -n +6 outputs lines starting from line 6, i.e., files older than the 5 newest. xargs rm -f deletes those files.

2. Step 2: Check other options

   ls -1t logfile-*.log.gz | head -n +6 | xargs rm -f deletes the first 6 newest files (wrong). ls -1 logfile-*.log.gz | tail -n 5 | xargs rm -f deletes last 5 files by name order, not time. ls logfile-*.log.gz | grep -v 'logfile-*.log.gz' | xargs rm -f uses grep incorrectly and does not select older files.

3. Final Answer:

   ls -1t logfile-*.log.gz | tail -n +6 | xargs rm -f -> Option A

4. Quick Check:

   Keep 5 newest, delete older = tail from 6th [OK]

Hint: Use ls -t and tail +6 to delete older files beyond 5 [OK]

Common Mistakes:

• Using head instead of tail to select files
• Deleting newest files instead of oldest
• Not sorting files by modification time