OneLinersCommand workbench
Verified diagnostic signature

Apache could not connect to or read a valid response from a proxied backend.

Match output from apache-httpd, understand the likely cause, then continue with sourced, read-only checks.

Confidence
high
Platforms
linux
Verified
2026-07-24
Recognized output

Signature matched locally

AH00957: .* attempt to connect .* failed

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Likely causes

What usually produces this signal

  1. Backend unavailable
  2. Connect or response timeout
  3. Wrong proxy target
  4. Protocol mismatch
Safe next checks

Collect evidence before changing the system

01

Fetch only the HTTP response headers

curl -I <url>

The output matches the expected target and exits without an error.

02

List listening TCP ports and their processes

lsof -iTCP -sTCP:LISTEN -n -P

The output matches the expected target and exits without an error.

03

Check whether a TCP port accepts connections

nc -vz <host> <port>

The output matches the expected target and exits without an error.