upx

Ultimate Packer for eXecutables

TLDR

Compress executable

$ upx [program]

Compress with best ratio

$ upx --best [program]

Compress with fastest speed

$ upx -1 [program]

Decompress executable

$ upx -d [program]

Test compressed file

$ upx -t [program]

List compression info

$ upx -l [program]

Keep backup

$ upx -k [program]

Compress quietly

$ upx -q [program]

Compress to a different output file

$ upx -o [packed_program] [program]

SYNOPSIS

upx [-d] [-t] [-l] [--best] [-1..-9] [options] files

upx (Ultimate Packer for eXecutables) compresses executables. Compressed programs decompress in memory when run.Compression reduces file size significantly, often 50-70% for binaries. This saves disk space and download bandwidth.The compressed executable is self-extracting. It decompresses to memory at load time without user intervention.Multiple executable formats are supported: Linux ELF, Windows PE, macOS Mach-O, and others.Decompression is fast with minimal runtime overhead. The original executable behavior is preserved exactly.Testing verifies compressed files are valid. This catches corruption before deployment.

PARAMETERS

-1 to -9

Compression level (1=fast, 9=best).

--best

Alias for -9, best compression ratio.

--brute

Try all compression methods and filters (very slow).

--ultra-brute

Even more exhaustive search (extremely slow).

-d

Decompress.

-t

Test integrity.

-l

List compression info.

-k

Keep backup file.

-o FILE

Output to file.

-f

Force compression.

-q

Quiet mode.

-v

Verbose mode.

--no-backup

Don't create backup.

--lzma

Use LZMA compression (better ratio but slower decompression).

--no-lzma

Disable LZMA compression (overrides --brute and --all-methods).

--overlay=ACTION

Handle overlay data: copy (default), strip.

CAVEATS

Some security tools flag UPX-compressed files. Code signing may be invalidated. Slight startup overhead from decompression. Some formats not supported.

HISTORY

UPX was created by Markus Oberhumer, László Molnár, and John Reiser in 1996. It became the standard tool for executable compression, widely used for software distribution.

upx