tail

Overview

The tail command outputs the last part of files. It’s particularly useful for monitoring log files and viewing recent changes.

Syntax

tail [options] [file...]

Common Options

Option Description
-n num Output last num lines
-f Follow file growth
-F Follow and retry if file inaccessible
-c num Output last num bytes
-q Never output headers
-v Always output headers
--pid=PID With -f, terminate after PID dies
--retry Keep trying to open file
--max-unchanged-stats=N Reopen file after N iterations

Key Use Cases

  1. Monitor log files
  2. View recent changes
  3. Follow file updates
  4. Debug applications
  5. System monitoring

Examples with Explanations

Example 1: View End

tail file.log

Show last 10 lines

Example 2: Follow Updates

tail -f log.txt

Monitor file for new content

Example 3: Multiple Files

tail -n 5 file1 file2

Show last 5 lines of each file

Understanding Output

  • Default: 10 lines
  • With -f:
    • Real-time updates
  • With multiple files:
    • ==> filename <== headers
  • Error messages for:
    • File not found
    • Permission denied
    • File rotation

Common Usage Patterns

  1. Monitor logs:

    tail -f /var/log/syslog

  2. View recent changes:

    tail -n 50 file

  3. Follow multiple files:

    tail -f file1 file2

Performance Analysis

  • Efficient file following
  • Memory usage control
  • Inode monitoring
  • File rotation handling
  • Multiple file impact

Additional Resources

Best Practices

  1. Use -F for log monitoring
  2. Consider log rotation
  3. Set appropriate buffer size
  4. Use with grep for filtering
  5. Monitor resource usage