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UPX

B
B tier on Executable PackersScore 7.0 · #3 of 27
Android app
Not listed
Free plan
Yes
Runs on
Linux, Mac, Windows
upx.github.io
The UPX homepage
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Summary

UPX is a portable tool for compressing and packing executable programs and libraries on Windows, macOS, and Linux. The project says it commonly reduces program and DLL file sizes by around 50%–70%. For most supported formats, packed files remain self-contained and run as before without runtime or memory penalties. UPX handles Windows programs and DLLs, macOS apps, and Linux executables, as well as formats such as PE, ELF, Mach-O, COFF, DOS, and Atari/TOS. It can list, test, and unpack files, and it keeps checksums for both compressed and original versions. The software is free under GPL v2 or later; a special exception allows unmodified UPX to compress commercial programs. UPX is not a protection or encryption tool, and its maintainers advise using it only with trusted files. Linux users should account for format-specific tradeoffs: compressed executables may require more RAM or swap when multiple processes run, and the generic Linux format recreates the original in /tmp before launch. The project is maintained by the UPX Team and accepts bug reports through GitHub issues.

Who it is for

UPX is for users who need to reduce executable file sizes or inspect and restore packed files across supported operating systems. Linux users should consider the documented runtime and temporary-file behavior.

What is good

  • Typically reduces program and DLL sizes by around 50%–70%.
  • Packed programs are self-contained for most formats.
  • Can list, test, and unpack executables.
  • Free software under GPL v2 or later.
  • Supports Windows, macOS, Linux, DOS, and Atari formats.

What to know first

  • It does not provide protection or encryption.
  • Use is advised only for trusted files.
  • Concurrent Linux processes may need more RAM or swap.
  • Generic Linux format creates a copy in /tmp.

Verdict

UPX offers executable compression and inspection tools across several operating systems and formats. It is not a security layer, and Linux users should account for its stated memory and temporary-file caveats.

UPX plans and pricing

All plans
UPX Free Free software under GPL v2+; special license exception permits use with commercial programs upx.github.io · 30 Sept 2026

Compared on executable packers

Free plan
Yesupx.github.io
Supported platforms
Windows, macOS, Linuxupx.github.io
Binary formats
PE, ELF, Mach-O, COFF, DOS/COM, DOS/EXE, DOS/SYS, Atari/TOSupx.github.io
Compression levels
advancedupx.github.io
Protection features
Noupx.github.io
Architecture support
multi-architectureupx.github.io
License model
perpetualupx.github.io

Facts

Purpose
UPX is a portable executable packer and file compressor for several executable formats.upx.github.io · 30 Sept 2026
Compression
The project says UPX typically reduces program and DLL file sizes by around 50%–70%.upx.github.io · 30 Sept 2026
Runtime behavior
Compressed programs are self-contained and run as before with no runtime or memory penalty for most supported formats.upx.github.io · 30 Sept 2026
Supported executable formats
UPX supports formats including Windows programs and DLLs, macOS apps, and Linux executables.upx.github.io · 30 Sept 2026
Inspect and restore
UPX can list, test, and unpack executables, and internally maintains checksums of compressed and uncompressed files.upx.github.io · 30 Sept 2026
License
UPX is distributed with full source under GPL v2 or later, with a special exception allowing unmodified UPX to compress commercial programs.upx.github.io · 30 Sept 2026
Security handling
The project warns that UPX inherits the security context of files it handles and says to use it only on trusted files.github.com · 30 Sept 2026
Security limits
UPX describes itself as a packer and explicitly says it will not add protection or encryption features.github.com · 30 Sept 2026
Linux runtime tradeoff
The documentation says compressed Linux executables do not share RAM at runtime like file-mapped executables, so concurrent processes may need more RAM or swap.github.com · 30 Sept 2026
Linux temporary files
For its generic Linux format, UPX recreates a copy of the original file in /tmp before running it.github.com · 30 Sept 2026
Download platforms
The latest release page provides Linux and Windows binaries, DOS builds, and a source tarball; it says each build handles all supported executable formats.github.com · 30 Sept 2026
Support
The project asks users to report bugs through its GitHub issues page.github.com · 30 Sept 2026
Maker
The homepage says UPX is maintained by the UPX Team and credits Markus F.X.J. Oberhumer, László Molnár, and John F. Reiser.upx.github.io · 30 Sept 2026

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