gzip file signature
Magic number at the start of the file
A gzip stream starts with the two bytes 1F 8B, then the compression method (08 for DEFLATE). Most .tar.gz and .tgz files are a tar archive wrapped in gzip, so the outer signature is this one.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 1F 8B, it is a gzip file.
Formats that use the 1F 8B signature
These file types in our database carry this signature:
It is also seen in: GZ, TGZ, SVGZ.
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.tar
- hexdump -C -n 16 example.tar
- file example.tar
Windows (PowerShell)
- Format-Hex -Path example.tar -Count 16
Python
- open("example.tar","rb").read(2).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the gzip file signature?
gzip files start with the hex bytes 1F 8B. This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.tar on Linux or macOS, or Format-Hex -Path example.tar -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the gzip signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine gzip file has these exact bytes; a file with the wrong bytes is not really gzip, whatever its name says.