cant create usb with catalina macos

[catalina&me]

Hi everyone,
i need help to test my imac memories with memtest86. i didnt manage to create the bootable usb key using the how to coming with the the zip.
i use dd if=(path of the dmg )drag an d drop make sure the path is correct , copy the dmg on the desktop always got a : no such file or directory
the usb key is format in mac os extended file manager ...

thx.

[David (PassMark)]

The procedure for a Apple Mac install of MemTest86 is.

Step 1
Download the current Memtest86 package as a Zip file from this page.
https://www.memtest86.com/download.htm


Step 2
Unzip the file. Inside the Zip there is a "disk image" file. For the free edition of MemTest86, this file is called, memtest86-usb.img


Step 3
Insert a USB flash drive into a USB slot. It needs to be at least 512MB in size. Warning: The contents will be overwritten in the next steps.


Step 4
Determine which device the USB drive is assigned as by opening the Terminal and typing the following command. Don't get this wrong as you don't want to overwrite the wrong drive.

diskutil list




Step 5
Unmount all volumes on the USB drive by typing the following command:

diskutil unmountDisk <device_name>

In the example above the device name is /dev/disk2


Step 6
As the root user, use the 'dd' command to write the image to the USB drive. For example,

sudo dd if=memtest86-usb.img of=<device_name> bs=4M

where <device_name> is the device the USB key is assigned to. Use the base device (ie. /dev/disk2) not a partition designation (ie. /dev/disk2s1). BS=4M means to use a read / write block size of 4MB, which is faster than the default 512bytes.

Warning: all data on the USB key will be lost.
3rd warning !!!! Make sure that the device used in the dd command above is correct. The consequence of picking the wrong drive are potentially disastrous. Total and compete data loss from your hard drive, if you overwrite the wrong drive.


Step 7 - Boot Memtest86
When finished, Reboot your On a Mac, you need to hold down the ALT / Option key on the Mac keyboard while powering on the machine to boot from USB.

On newer Macs (from 201 with the Apple T2 Security Chip, you may need to change the SecureBoot settings for MemTest86 to boot. Please see the following page for instructions:
https://support.apple.com/en-us/HT208330

[catalina&me]

still got no such file or directory....

[David (PassMark)]

i use dd if=(path of the dmg )

I think you are confused on this point. There is no DMG file involved in this process. DMG files are containers for Mac desktop apps. But this isn't what MemTest86 is.

still got no such file or directory

I assume that error was on the dd command?

If means the input file (if) or output file (of) was not found on your sytem.
dd if=memtest86-usb.img of=<device_name>

So you need to figure out what folder you have placed the .img file into and then use the correct path to the .img file. I've no idea where you might have saved it, but it might be something like.
dd if=/myfolder/subfolder/memtest86-usb.img of=/dev/disk2

If you have folder names with space characters in them, then quotes are required.
dd if='/my folder/sub folder/memtest86-usb.img' of=/dev/disk2

[catalina&me]

im sorry my mistake i write dmg instead of img.
to make sure the correct path of the memtest86.img is entered i use the drag and drop option
i think the problem is the output directory , im not sure if i have to format the usb key before and what file format to chose (fat, afps , hfs..)

[David (PassMark)]

There is no output directory. There is an output device, but not a directory.
The output device doesn't need to be formatted, as it will be completely overwritten. Any existing formatting will be overwritten and replaced.

[catalina&me]

i tried again , and now i have files in the usb device . But when i power on the computer and holding option , there is no memtest on the menu.
any idea why ?

[Richard (PassMark)]

On a Mac, you need to hold down the ALT / Option key on the Mac keyboard while powering on the machine to boot from USB.

On newer Macs, from around 2019(*), with the Apple T2 Security Chip, you may need to change the SecureBoot settings for MemTest86 to boot. Please see the following page for instructions:
https://support.apple.com/en-us/HT208330


(*) These Mac computers have the Apple T2 Security Chip:

• iMac introduced in 2020
• iMac Pro
• Mac Pro introduced in 2019
• Mac mini introduced in 2018
• MacBook Air introduced in 2018 or later
• MacBook Pro introduced in 2018 or later

Allow booting from external drives and allow booting from non-apple software,

[catalina&me]

i recently did a clean install with a usb device ( no problem to access to the boot menu and start catalina installation) to see corrupted files system could be the problems , no chance
thats why i want to test memory module...

[rperchonok]

I am also unable to create a bootable USB flash drive for my iMac 2020 (Apple T2 security chip). I believe that I have followed the directions provided in this forum and at https://www.memtest86.com/tech_creating-linux-mac.html. A few observations:

• Steps 1 & 2. Completed without a problem.
• Step 3. My flash drive is USB 3.1 128GB.
• Step 4. The terminal command "diskutil list” clearly shows my flash drive is assigned "/dev/disk4”.
• Step 5. I am able to successfully unmount my flash drive. My terminal session confirms this and the drive no longer appears in Finder.
• Step 6.
• • I first cd to the directory where memtest86-usb.zip was unzipped.
  • I confirm with the ls command that the directory contains the file memtest86-usb.img.
  • I issue the command "sudo dd if=memtest86-usb.img of=/dev/disk4"
  • When prompted for a password, I provide that associated with the administrator privileged account that I am logged into.
  • After a 14 minute wait, the copy appears to succeed with the following terminal message:
  • • 1024000+0 records in
    • 1024000+0 records out
    • 524288000 bytes transferred in 592.901005 secs (884276 bytes/sec)
• Step 7. When booting my iMac while holding the Option key down, I now see two additional boot devices both labeled “EFI Boot”. I separately tried booting from each, but in both cases receive the error message: "Unable to verify startup disk. Try again or select another startup disk.”
• • I have confirmed that I had previously set the External Boot option (in Startup Security Utility) to Allow booting from external media. I know this works in that I’ve previously booted from a duplicate external bootable drive created by SuperDuper.

Any suggestions for how to proceed?
Thanks,
Bob

[David (PassMark)]

884276 bytes/sec

This is 0.8MB/sec. USB3 speeds should be more around 100MB/sec. Are you sure there isn't something wrong with the flash drive.

On newer Macs, from around 2019 with the Apple T2 Security Chip, you may need to change the SecureBoot settings for MemTest86 to boot. Please see the screen shot in post above & following page for instructions:
https://support.apple.com/en-us/HT208330

[catalina&me]

if that can help





so i assume the usb device is done , and my imac doesnt have t2 chip
still not able to boot from the usb device , there is no usb device during the boot menu
thanks.

[rperchonok]

On further review, my 128GB flash drive was formatted as a 260.8 MB MS-DOS (FAT16) drive as a result of the “sudo dd” command. Of that space, only 7.9 MB is in use. However, the message provided in Terminal in response to the “sudo dd” command indicated that 524 MB were transferred. See my previous posting. What is the expected size and content of the USB flash drive after executing the "sudo dd" command?

In order to confirm the typical transfer speeds to my USB flash drive, I reformatted it as Mac OS Extended and copied a 1GB file to it from my iMac. The copy required 14sec, i.e. an estimated speed of 71MB / sec.

As I stated in my first posting, I have confirmed that the External Boot option (in Startup Security Utility) is set to Allow booting from external media. I’ve also confirmed that I can boot my iMac using a Thunderbolt 3 external drive.