Linux Survival Basics

Find the Exact Log Line Before You Scroll

A log file contains likely failures, but you need line numbers so you can inspect context around the match.

Command

grep -inE 'error|failed|denied|timeout' /var/log/nginx/error.log

What changed

Nothing changes. The command prints matching lines with line numbers for follow-up inspection.

Danger

safe

When to use it

Use this when a first-pass grep finds failures and you need the surrounding context next.

When not to use it

Do not assume these four words catch every failure; applications often log custom error language.

Undo or recovery

No state is changed.

Expected output

Matching log lines prefixed by their line numbers.

demo script

Disposable terminal steps

grep -inE 'error|failed|denied|timeout' /var/log/nginx/error.log
grep -inE 'error|failed|denied|timeout' /var/log/nginx/error.log | tail -20
sed -n '2,5p' /var/log/nginx/error.log

Terminal transcript Demo JSON

simulated output

What it looks like

disposable vessel

::fixture-ready::
$ grep -inE 'error|failed|denied|timeout' /var/log/nginx/error.log
2:2026/06/25 10:01:42 [error] 11#11: *7 connect() failed (111: Connection refused) while connecting to upstream
4:2026/06/25 10:03:16 [error] 11#11: *9 access forbidden by rule, client: 203.0.113.44
5:2026/06/25 10:04:33 [error] 11#11: *10 upstream timed out while reading response header
::exit-code::0
$ grep -inE 'error|failed|denied|timeout' /var/log/nginx/error.log | tail -20
2:2026/06/25 10:01:42 [error] 11#11: *7 connect() failed (111: Connection refused) while connecting to upstream
4:2026/06/25 10:03:16 [error] 11#11: *9 access forbidden by rule, client: 203.0.113.44
5:2026/06/25 10:04:33 [error] 11#11: *10 upstream timed out while reading response header
::exit-code::0
$ sed -n '2,5p' /var/log/nginx/error.log
2026/06/25 10:01:42 [error] 11#11: *7 connect() failed (111: Connection refused) while connecting to upstream
2026/06/25 10:02:05 [warn] 11#11: upstream server temporarily disabled
2026/06/25 10:03:16 [error] 11#11: *9 access forbidden by rule, client: 203.0.113.44
2026/06/25 10:04:33 [error] 11#11: *10 upstream timed out while reading response header
::exit-code::0

YouTube Short

Find the exact log line first.

Line numbers make log debugging faster. First find the failure, then inspect the few lines around it instead of scrolling forever.

experiments

A/B tests to run

Metric: linkedin_save_rate

A: Find the exact log line before you scroll.

B: Use `grep -n` before reading the whole log.