Quick Techniques for Locating Errors in Large Log Files Using Linux Commands

The author, an architect who writes code and poetry, shares practical ways to quickly locate errors in large log files.

Dynamic log viewing : Use tail -f catalina.out to follow a log in real time, or cat catalina.out to display the whole file. You can also redirect a specific log segment to a file with cat -n catalina.out | grep 717892466 > nanjiangtest.txt .

Simple tail/head commands :

tail -n number catalina.out          # show the last *number* lines
tail -n +number catalina.out          # show 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 then extract surrounding lines :

First obtain the line number of the keyword with cat -n test.log | grep "关键词" . Then retrieve context, for example:

cat -n catalina.out | tail -n +13230539 | head -n 10

Method 2 – Query a specific time range :

grep '11:07 18:29:20' catalina.out
grep '11:07 18:31:11' catalina.out

Or use sed -n '/11:07 18:29:20/,/11:07 18:31:11/p' catalina.out to extract the whole interval.

Method 3 – Count occurrences of a string :

grep '1175109632' catalina.out | wc -l

Method 4 – Show the last *N* lines and filter a keyword :

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

Method 5 – Highlight matches with color :

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

Method 6 – Show matches with surrounding lines (two lines of context):

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

Method 7 – Paginate results using more or less :

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 for less :

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 article concludes with an invitation to join a community of architects and a reminder that sharing the post provides strong support.