-ssw (Compress files open for writing) switch

Compresses files open for writing by another applications. If this switch is not set, 7-zip doesn't include such files to archive.

Syntax

-ssw

Example

7z a archive.7z -ssw *.txt

compresses all *.txt files in current folder including files open for writing by another applications.

Commands that can be used with this switch

a (Add), h (Hash), u (Update)

Notes from this site

Not part of the 7-Zip manual. Written by this site; examples checked with 7-Zip 26.04.

How do I back up files that are in use?

The switch is -ssw; the page address says "shared". On Windows, a program that has a file open can keep other programs from reading it. Without -ssw, 7-Zip skips such files and reports a warning. With -ssw, it adds them anyway. It works with a, u and h (hash).

7z a "D:\Backup\my backup.7z" "C:\My Data\*" -ssw
7z h -ssw "C:\Data\*.mdb"

Quote any path with spaces (the same in cmd.exe and PowerShell). The second line hashes files that are open. The official Linux/macOS console binary is 7zz. There the switch is accepted (7zz a backup.7z "data/*.txt" -ssw and 7zz h -ssw "data/*.txt" finished with exit code 0), but the manual describes it for files open in another application on Windows, and we saw no difference.

Good to know

Skipped files are named in the output. In our macOS test with an unreadable file, 7-Zip ended with a WARNINGS for files: list naming it and exit code 1 (warning). Check the code in scripts (%errorlevel% in cmd.exe, $LASTEXITCODE in PowerShell); see exit codes.
-ssw is not a snapshot. The file is read while the other program may still be writing to it, so the copy in the archive can mix old and new data. For databases and mail files, close the program first.
To leave known busy files out instead, use -x.