TAR Archive MIME Type

What does application/x-tar mean?

The application/x-tar media type identifies a TAR archive, normally named with the .tar extension. TAR stores a sequence of files and filesystem metadata in one byte stream. It can preserve directories, permissions, timestamps, symbolic links, hard links, user and group information, and some special file types.¹

The media type is widely used but not registered with IANA. IANA's application registry has no application/x-tar entry, while MDN documents it as the conventional type for .tar files.²³ The historical x- prefix does not make TAR experimental, and RFC 6838 no longer treats such prefixes as a formal unregistered tree.⁴

Why is the TAR format not just one layout?

Early Unix tar implementations wrote what is now called the V7 format. POSIX standardized the extended ustar interchange format in 1988, keeping older archives readable while adding fields such as user and group names and a pathname prefix. POSIX later defined the pax format, which keeps the ustar physical layout and uses extended header records for values that do not fit its fixed fields.¹⁶

GNU tar describes ustar as a sound choice for interchange with other implementations. Its posix format is more flexible, including support for long names and large values, but very old readers may not interpret every extension correctly. GNU's historical native format also differs from current POSIX in some header fields.⁶

The MIME type does not identify which layout an archive uses. A recipient still needs a TAR reader that understands the archive's particular headers and extensions.

How do you identify a TAR archive?

A TAR archive is organized into 512-byte blocks. Each member starts with a header containing its pathname, mode, owner IDs, size, modification time, type, link target, and a header checksum. File data follows and is padded to the next 512-byte boundary. A conforming pax archive ends with two all-zero blocks.¹⁷

There is no signature shared by every TAR variant, so this page does not claim one universal magic number. In a ustar header, the ASCII text ustar begins at byte offset 257, but V7 archives do not have that field. A robust detector should validate the complete header, its numeric fields, and its checksum instead of looking only for an extension or five bytes.¹⁷

How do you open an application/x-tar file?

Browsers do not provide a native TAR member viewer. They usually download the response for a local archive tool.

GNU tar and libarchive's bsdtar can list, create, and extract TAR archives. Windows also includes a tar command based on libarchive, with support for .tar and common compressed archive combinations.⁶⁸

List an unfamiliar archive first:

tar -tvf archive.tar

Then extract it into a new, empty directory:

mkdir unpacked
tar -xf archive.tar -C unpacked

GNU tar can recognize several common compression formats and call the corresponding decompressor. A plain .tar remains uncompressed, so adding .gz or .xz to its filename does not compress it.⁵

Support in Poly

Poly maps .tar filenames to application/x-tar and classifies the result as an archive. It can store, sync, share, version, download, and find the outer file by name.

Poly does not process the TAR payload itself:

• It does not list or extract archived members.
• It does not index member names, metadata, or contents.
• It does not generate a thumbnail or offer an in-app archive preview.
• The Poly agent cannot inspect files held inside the archive.

The filename mapping uses the last extension. Poly recognizes a plain backup.tar as TAR. For backup.tar.gz, the final .gz maps to Gzip, and Poly still does not inspect the TAR stream inside it. Upload extracted files separately when you want each supported member to be previewed or indexed.

TAR versus ZIP

TAR and ZIP can both bundle directory trees, but their designs suit different jobs.

Choose TAR when Unix metadata and streaming workflows matter. ZIP is often simpler when recipients need one broadly familiar compressed file. Converting between them means extracting and repacking, which can lose ownership, permissions, hard links, symbolic links, special files, or format-specific metadata.

Security and privacy considerations

A TAR header can name absolute paths, parent directories, symbolic links, device nodes, executable files, ownership, and permissions. Careless extraction can therefore overwrite files or place content outside the intended directory. GNU tar recommends extracting each untrusted archive into its own empty directory and warns that --absolute-names can let archive paths overwrite any writable location.⁹

Inspect the member list, extract as an unprivileged user, and review the result before moving it into a trusted location. Do not restore owner IDs, permissions, devices, or links unless the workflow requires them.

TAR does not authenticate its creator, and its header checksum is not a cryptographic integrity check. Use a separately authenticated signature or digest when provenance matters. Archives can also reveal filenames, account names, timestamps, permissions, and directory structure even when the member contents are not opened.