Quick reference for sha1sum, a tool to compute and verify SHA-1 checksums. SHA-1 is considered weak for modern security; use it mostly for legacy compatibility, not new designs.

Basic usage

• sha1sum file.img – print SHA-1 hash and filename.
• sha1sum file1 file2 – hash multiple files.
• echo -n "test" | sha1sum – hash data from stdin.

Common options

• -b – read files in binary mode (default on Linux).
• -t – read files in text mode (mainly for non-Unix systems).
• -c – check SHA-1 sums from a file.
• --tag – create BSD-style output (SHA1 (file) = hash).

Creating and verifying checksum files

• sha1sum file.img > file.img.sha1 – save checksum.
• sha1sum file1 file2 > checksums.sha1 – create checksum list.
• sha1sum -c file.img.sha1 – verify a single file.
• sha1sum -c checksums.sha1 – verify multiple files.

Tips

• Prefer sha256sum or sha512sum for security-sensitive uses.
• Use SHA-1 mainly when you must match existing ecosystems or published hashes.
• Keep checksum files alongside downloads so users can verify integrity easily.