FAQ
Frequently asked questions
Grouped by topic instead of one long numbered list — click a question to expand it.
User FAQ
Licensing & use
Can I use 7-Zip in a commercial organization?
Yes. It's free software, usable on any computer without registration or payment — including commercial use.
Archives & compatibility
Why can 7z archives created by new versions of 7-Zip be larger than those from old versions?
Since version 15.06, 7-Zip sorts files "by name" instead of the older "by type" order by default, which can reduce compression for solid archives with a small dictionary. Use the "qs" switch or a larger dictionary to recover the old ratio.
Why can't 7-Zip open some ZIP archives?
Usually the archive has faulty headers that more lenient programs silently ignore, or it uses a compression method 7-Zip doesn't support, such as WavPack.
Why can't 7-Zip open some RAR archives?
Version 9.20 only supports RAR 2/3/4, not RAR5 — newer 7-Zip releases do support RAR5.
Why does drag-and-drop extraction from 7-Zip to Explorer use temp files?
7-Zip doesn't know the exact drop destination in advance, so it extracts to a temp folder first and lets Explorer move the files from there.
Why can't 7-Zip use a big dictionary on 32-bit Windows?
32-bit Windows limits an application to 2 GB of fragmented virtual address space. 64-bit Windows removes that limit.
How can I recover a corrupted 7z archive?
There's a separate recovery guide for archives showing CRC/data errors or that fail to open at all — see the official site for the full steps.
Command line
Why doesn't the command line version add files without extensions?
The "*.*" wildcard only matches files that have an extension. Use "*" instead to match everything.
Why doesn't the -r switch work as expected?
7-Zip already compresses subfolders by default without -r. That switch instead triggers a recursive search across all matching subfolders, which can pull in more than you intended.
How can I store the full path of a file in an archive?
7-Zip only stores relative paths. Change the working directory to a common parent folder before archiving with relative paths.
How can I install 7-Zip in silent mode?
For the EXE installer, use /S and /D=<path>. For the MSI installer, use /q and INSTALLDIR=<path>.
Windows setup
How can I set file associations to 7-Zip in Windows 7 and Windows Vista?
Run the 7-Zip File Manager as administrator (right-click → Run as administrator) to change file associations and other options.
Developer FAQ
Why are there linking errors compiling with Visual C++ 6.0?
You need the matching Platform SDK version (the Windows Server 2003 PSDK from February 2003) — newer SDKs aren't compatible with MSVC6.
Can I use the EXE or DLL files in a commercial application?
Yes, as long as your documentation credits 7-Zip's use, notes the GNU LGPL license, and links to www.7-zip.org.
How can I add support for 7z archives to my application?
Use 7z.dll / 7za.dll via its COM-style interfaces, or call the command-line 7za.exe directly.
Can I use the source code of 7-Zip in a commercial application?
The LGPL permits modification, but any modified library code must stay under LGPL/GPL — separate application code linking to it can use any license. The LZMA SDK offers more flexible terms if that's a better fit.