Web Server Rescue
Read-onlyYour Site Is Not Down. DNS Might Be Lying.
A domain appears unreachable, but you need to separate a real server outage from stale or wrong DNS.
Command
curl --resolve example.com:443:203.0.113.10 https://example.com/Before you run this
System impact: Read-only. Low when scoped to the shown target.
When not to use it: Do not treat a successful forced request as proof that public DNS is correct. Do not use it to test someone else's service without permission.
Expected output
HTTP response headers or page content from the target server. The lab example uses a local test service on port 8443; a real web server normally uses 443.
System impact
Read-only. The request bypasses normal DNS for one call and tests the HTTPS server directly. The temporary shell lab uses a local test service so it stays offline and deterministic.
When to use it
Use this when DNS, browser cache, router DNS, or CDN routing may be hiding the real server state. In production, replace the example domain and IP with the host you control.
When not to use it
Do not treat a successful forced request as proof that public DNS is correct. Do not use it to test someone else's service without permission.
Recovery / rollback
No system state is changed. Remove the forced IP and test normal DNS again.
Watch this command run
Command transcript
This sanitized transcript shows the commands and output shape without exposing host details.
$ dig +short example.com
198.51.100.44$ curl -k -sS --max-time 2 -D - -o /dev/null https://localhost:8443/
HTTP/1.0 200 ok
Content-type: text/html
$ curl -k -sS --max-time 2 --resolve example.com:8443:localhost -D - -o /dev/null https://example.com:8443/
HTTP/1.0 200 ok
Content-type: text/html
View commands shown
These are the commands shown in the sanitized transcript.
Commands shown
dig +short example.comcurl -k -sS --max-time 2 -D - -o /dev/null https://127.0.0.1:8443/curl -k -sS --max-time 2 --resolve lab.local:8443:127.0.0.1 -D - -o /dev/null https://lab.local:8443/
next steps
Related commands
Smoke Check an HTTP Status
A deploy is not done until the endpoint answers.
curl -fsS -o /dev/null -w '%{http_code} %{time_total}s\n' https://example.com/health
Inspect Response Headers
The page loaded, but the headers told the operational story.
curl -sI https://example.com
Check HTTP to HTTPS Redirect
HTTPS worked. The plain HTTP redirect still mattered.
curl -I http://example.com
Check a Domain A Record
The site was fine. The domain was pointed somewhere else.
dig +short example.com A
Check the Certificate Served for SNI
The IP was right. The SNI name selected the wrong certificate.
openssl s_client -connect 203.0.113.10:443 -servername wrong.edge.test </dev/null 2>/dev/null | openssl x509 -noout -subject -ext subjectAltName
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.
Useful for
- LPIC-1 style command-line practice
- LFCS style performance tasks
- Linux+ style troubleshooting review
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.