file command in Linux: determining file type, examples

Q: "Script won't run: cannot execute binary file"

file script shows the real type. Common causes: it's HTML/an error page instead of a binary (the wrong thing got downloaded), or CRLF line endings (file will say "with CRLF line terminators") — fix it with sed -i 's/\r$//' script.

Q: The text encoding is in question

file -i file shows the charset (utf-8 / iso-8859-1). Use iconv to re-encode it.

Q: Determining the filesystem type on a partition

file -s /dev/sdXN (as root) is a quick way without mounting; for partitioning, see mount.

Q: file says "data" instead of a specific type

No signature matched in the /etc/magic database — either the file is corrupted, or it's an unknown/raw format (for instance, encrypted data looks like a random byte stream). That's not a file error but an honest "couldn't identify it".

Overview

file determines a file's type by its content (a signature, "magic bytes"), not by its extension. On Linux the extension means nothing — file tells the truth.

bash

file report           # report: ASCII text
file /bin/ls          # ELF 64-bit LSB pie executable, x86-64 …
file archive          # gzip compressed data  (even without a .gz extension)
file photo            # JPEG image data, …

file matches against a database of signatures (/etc/magic, the file/libmagic package) rather than guessing from the extension — renaming a file to .txt won't change the result.

Options

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-b (brief, no filename), -i (MIME type and encoding), -L (follow a symlink and look at its target, not the link itself), -s (look inside special files/block devices — otherwise file just says "block special"), -z (look inside a compressed file instead of just identifying it's gzip).

Option	What it does	Example
`-b` `--brief`	Don't print the filename, only the type — handy in scripts.	`file -b script.sh`
`-i` `--mime`	MIME type and encoding instead of a human-readable description.	`file -i notes.txt`
`-L` `--dereference`	Follow a symlink and inspect its target, not the link itself.	`file -L symlink`
`-s` `--special-files`	Look inside special files and block devices (otherwise just "block special").	`file -s /dev/sda1`
`-z` `--uncompress`	Look inside a compressed file to determine the content type, not just the compression format.	`file -z archive.gz`

Nothing found. Try a shorter query.

Recipes

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Examples

bash

file *                        # types of every file in a directory
file -i notes.txt             # MIME type: text/plain; charset=utf-8
file -b script.sh             # no filename (type only) — handy in scripts
file -L symlink               # follow the symlink and look at the target
file -s /dev/sda1             # -s: look inside a block device (filesystem type)
file -z archive.gz            # look INSIDE a compressed file

Troubleshooting

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"Script won't run: cannot execute binary file"

file script shows the real type. Common causes: it's HTML/an error page instead of a binary (the wrong thing got downloaded), or CRLF line endings (file will say "with CRLF line terminators") — fix it with sed -i 's/\r$//' script.

The text encoding is in question

file -i file shows the charset (utf-8 / iso-8859-1). Use iconv to re-encode it.

Determining the filesystem type on a partition

file -s /dev/sdXN (as root) is a quick way without mounting; for partitioning, see mount.

file says "data" instead of a specific type

No signature matched in the /etc/magic database — either the file is corrupted, or it's an unknown/raw format (for instance, encrypted data looks like a random byte stream). That's not a file error but an honest "couldn't identify it".

file — determining file type

Cheat sheet