So today, I am trying to compress multiple folders, of old photos which I want to backup.

I've found this article, that says method PPMd, and compression level Ultra, are far better for image compression.

The command I'm executing is: 7z a ./output.7z /path/to/dir1/ /path/to/dir2/ -m=PPMd -mx=9

And the output has an error E_INVALIDARG:

7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,64 bits,4 CPUs Intel(R) Core(TM) i7-5500U CPU @ 2.40GHz (306D4),ASM,AES-NI)

Scanning the drive:
2 folders, 318 files, 1421027053 bytes (1356 MiB)

Creating archive: ./output.7z

Items to compress: 320

System ERROR:

The thing I don't understand is, since the man page, has the -m | METHOD parameter, and the -mx | Compression Level parameter, it stills throws an error.

Any help is greatly appreciated. Thank you, Damian G.

* Note: My OS is Ubuntu 19.04 x86_64*
* Bash Version is 5.0.3(1)-release *


The correct use is

7z a ./output.7z /path/to/dir1/ /path/to/dir2/ -m0=PPMd -mx=9

Source: (Search for PPMd)

  • well, it works finally, thanks! – Damian G Sep 15 '19 at 10:28

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