upx

Compress executable

$ upx [program]

$ upx --best [program]

$ upx -1 [program]

$ upx -d [program]

$ upx -t [program]

$ upx -l [program]

$ upx -k [program]

$ upx -q [program]

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.

-1 to -9

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

Best compression.

Try all methods (slow).

Decompress.

Test integrity.

List compression info.

Keep backup file.

Output to file.

Force compression.

Quiet mode.

Verbose mode.

Don't create backup.

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

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

strip(1), gzip(1), objcopy(1)