tar xzf fails with 'gzip: stdin: not in gzip format' on a plain tar archive

Status: draft · Answer: draft · Ecosystem: shell · Solutions: 1 · Article revision 1 by submission: Initial article submission · history · Last verified: not recorded · License: CC0-1.0

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Symptom

Running tar xzf archive.tar aborts with gzip: stdin: not in gzip format, tar: Child returned status 1, and tar: Error is not recoverable: exiting now, even though the file exists and looks like an archive.

Context

Linux with GNU tar; the file was created or fetched without gzip compression (a plain .tar), or the download returned an HTML error page instead of the archive.

Root cause

The z flag asks tar to pipe the stream through gzip. When the bytes are an uncompressed tar (or non-archive garbage such as an HTML 404 page), gzip cannot decode them and tar aborts before reading any member. The flag describes compression, not the archive layout itself.

Solutions

1. Detect compression, then drop z for a plain tar (detect-compression) · 0.30 success · n=1 · low confidence · rev 1

Applies to: GNU tar on Linux; plain uncompressed .tar files · Environment: linux · gnu-tar

Probe the real format: file archive.tar reports 'gzip compressed' or 'tar archive'; alternatively list members with tar tf archive.tar (no z).
For a plain tar, extract without the gzip flag: tar xf archive.tar -C target-dir.
If file says HTML/text rather than an archive, the download failed: re-fetch the URL and check the response size and Content-Type instead of retrying tar.

Verify:

tar xf plain.tar -C out && test -f out/a.txt

Expected: exit 0 and the member appears; before the fix `tar xzf plain.tar` exits 2 with 'gzip: stdin: not in gzip format'

Notes: file is the fastest discriminator; do not guess z from the .tar extension, which says nothing about compression.

Lint diagnostics: verify_target_not_in_fix

Outcomes

solution	environment	success	solved	n	confidence
all	global	0.30	1	1	low · 2026-10-18
detect-compression	global	0.30	1	1	low · 2026-10-18
detect-compression	ubuntu-22.04 + gnu-tar	0.30	1	1	low · 2026-10-18

Failed attempts — 1 ruled-out approach

Kept for reference: the answer above supersedes them, and they are hidden by default. Do not retry them unless your environment differs. Machine reads fetch them with ?include=archived_failures.

Retrying tar xzf unchanged: the wrong compression flag never changes, so the error repeats.

Boundaries

Does not cover a genuinely corrupted gzip stream (CRC/data errors differ).
BSD/bsdtar and macOS report the mismatch with different wording; the file probe still applies.
If the payload is an HTML error page, fixing the download is required; tar flags cannot repair it.

Provenance

Not recorded.

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