Debian package file signature
Magic number at the start of the file · !<arch>
A Debian .deb package is a Unix ar archive, so it starts with the ASCII magic !<arch>. Inside are a version file and two compressed tarballs holding the control data and the payload.
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 21 3C 61 72 63 68 3E (the text !<arch>), it is a Debian package file.
What each byte of 21 3C 61 72 means
Here is the signature byte by byte, the way a hex editor shows it: the position in the file, the value in hex and in decimal, and the character that value stands for in ASCII. Bytes with no printable character show a dot.
| Byte offset | Hex | Decimal | ASCII |
|---|---|---|---|
| 0 | 21 | 33 | ! |
| 1 | 3C | 60 | < |
| 2 | 61 | 97 | a |
| 3 | 72 | 114 | r |
| 4 | 63 | 99 | c |
| 5 | 68 | 104 | h |
| 6 | 3E | 62 | > |
Formats that use the 21 3C 61 72 signature
These file types in our database carry this signature:
It is also seen in: AR, LIB.
How to check a file's signature
You can read the bytes of any file yourself. They are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.deb
- hexdump -C -n 16 example.deb
- file example.deb
Windows (PowerShell)
- Format-Hex -Path example.deb -Count 16
Python
- open("example.deb","rb").read(7).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the Debian package file signature?
Debian package files start with the hex bytes 21 3C 61 72 63 68 3E (!<arch> in ASCII). 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.deb on Linux or macOS, or Format-Hex -Path example.deb -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the Debian package signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine Debian package file has these exact bytes; a file with the wrong bytes is not really Debian package, whatever its name says.
Related signatures
Sources
Reuse this signature
This entry is part of the WhatFileType file signature reference, published under a CC BY 4.0 licence with the full provenance for every entry, a copy-paste embed and a JSON export. Credit WhatFileType and the data is yours to republish.