Quick Techniques to Pinpoint Errors in Massive Log Files

Dynamic Log Viewing

Use tail -f catalina.out to follow a log file in real time.

Open Log from Start

Display the entire file with cat catalina.out or redirect output to a new file for further analysis:

# cat -n catalina.out | grep 717892466 > nanjiangtest.txt

Basic tail/head Commands

tail -n number catalina.out

– show the last number lines. tail -n +number catalina.out – display from line number onward. head -n number catalina.out – show the first number lines. head -n -number catalina.out – show all but the last number lines.

Method 1: Find Line Numbers by Keyword

First obtain the line number containing a keyword, then extract surrounding lines:

# cat -n catalina.out | grep "keyword"
# cat -n catalina.out | tail -n +13230539 | head -n 10

Method 2: Search Within a Time Range

Use grep to verify timestamps, then extract the range with sed:

grep '11:07 18:29:20' catalina.out
sed -n '/11:07 18:29:20/,/11:07 18:31:11/p' catalina.out

Method 3: Count Occurrences of a Specific String

# grep '1175109632' catalina.out | wc -l
154

Method 4: Search the Last n Lines for a Keyword

# tail -n 20 catalina.out | grep 'INFO Takes:1'

Method 5: Highlight Matches

# tail -n 20 catalina.out | grep 'INFO Takes:1' --color

Method 6: Show Context Lines Around Matches

# tail -n 20 catalina.out | grep 'INFO Takes:1' --color -a2

Method 7: Paginated Viewing

Pipe the filtered output to more or less for page‑by‑page navigation:

# tail -n 2000 catalina.out | grep 'INFO Takes:1' --color -a2 | more
# tail -n 2000 catalina.out | grep 'INFO Takes:1' --color -a2 | less

Additional Navigation Shortcuts (within less/more)

ctrl + F

– forward one screen ctrl + B – backward one screen ctrl + D – forward half screen ctrl + U – backward half screen j – move down one line k – move up one line G – go to the last line g – go to the first line q or ZZ – quit the pager