Linux Survival Basics
Read-only, can be slowFind 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.logBefore you run this
System impact: Read-only. Can create load on large logs, directories, filesystems, or process tables.
When not to use it: Do not assume these four words catch every failure; applications often log custom error language.
Expected output
Matching log lines prefixed by their line numbers.
System impact
Read-only, can be slow. Nothing changes. The command prints matching lines with line numbers for follow-up inspection.
May require elevated permissions on protected paths or service-owned files.
Scope this to the smallest useful path or service on busy systems.
Recovery / rollback: no state is changed.
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.
next steps
Related commands
Find Errors Before Reading Every Log Line
The error was in the log. The problem was finding it without reading noise.
grep -iE 'error|failed|denied|timeout' /var/log/nginx/error.log | tail -40
Show Only Recent Errors
The log had old failures too. I only cared about the newest ones.
grep -iE 'error|failed|denied|timeout' /var/log/nginx/error.log | tail -10
Read Recent Nginx Error Log Lines
The error log often names the denied path.
sudo tail -80 /var/log/nginx/error.log
Watch Logs Without Opening the Whole File
The app was failing now. Opening a giant log file was the wrong move.
tail -n 80 -f /var/log/nginx/error.log
Find SSH Too Many Authentication Failures Lines
The auth log proves whether the server refused after too many offered keys.
grep -i 'Too many authentication failures' /var/log/auth.log /var/log/secure 2>/dev/null | tail -20
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.