try to convert MacOS iso file to img file in order to create a bootable USB key : hdiutil fails

Thanks for your reply.

It is exactly what I tried but without success. When you said open the .pkg, what do you mean. I tried to execute the .pkg to have the Installer "installed" on the Applications folder but it failed.

This MacOS version is not supported by your computer . The Mac I use to create a Sierra installer on USB... is running Big Sur.

any idea to move forward ?

After a couple of hours, I was able today to reinstall MacOS on my 2009 old Mac...after several other issues.

1) with the help of an 2015 MacBook Air, I was able to launch the PKG file to extract the Sierra Installer.

2) the createinstallmedia command line to create the key made me crazy because it failed at first attempt with an error. I solved the issue, thanks to @Eau Rouge by changing something inside the Sierra installer

sudo plutil -replace CFBundleShortVersionString -string "12.6.03" /Applications/Install\ macOS\ Sierra.app/Contents/Info.plist

then the USB was OK

3) I rebooted my old Mac with the USB key, the installation started then failed again with exactly the same error I had at the very beginning when trying to reinstall El Capitan on my old Mac

No packages were eligible for install !!!

After some research, the solution was to change the computer date before the install via the Terminal , I put 20 Aug 2018 (command line : date 0820140018) because with the Apple Sierra installation file there is a certificate which has expired today, so the solution is to simulate that you are in 2018.

And finally It worked !

Thanks to you guys

I am trying to follow this : https://www.lewan.com/blog/2012/02/10/making-a-bootable-usb-stick-on-an-apple-mac-os-x-from-an-iso, so the first step is the iso to img conversion

My old mac (2009) doesn't have any SSD drive, only a classic harddrive.

the stick is formated in the right MacOS format, the issue is not here as now, I am just trying to convert the iso file from my Mac.

I am trying to prepare a Sierra MacOS USB bootable key from my new Mac (Big Sur). I downloaded a Sierra ISO file , available now on my Download folder.

I tried before that to download the Sierra DMG file from App Store, I am then able to mount it and have the pkg file but after that, I am stuck because my Mac (Big sur) refuses to launch the pkg file in order to have the Sierra Installer in the Applications folders.

I'm going in circles ! with the 2 ways to create an USB key :-(

Whaou, thanks, I didn't know that and nothing like this was mentioned on Apple tech notes.

So I have one very old Mac (2009) for which I want to reinstall MacOS via USB , one too new Mac (2019)... and now I need to find a Mac "in the middle" which accept Sierra 10.12 or High Sierra 10.13 which are the last versions accepted by a late 2009 machine.

Thank you