OK, after unsuccessfully trying all methods mentioned here, I finally got it working. Basically, the missing step was to write a proper boot sector to the USB stick, which can be done from Linux with ms-sys or lilo -M. This works with the Windows 7 retail version.
Here is the complete rundown again:
Install ms-sys - if it is not in your repositories, get it here. Or alternatively, make sure lilo is installed (but do not run the liloconfig step on your local box if e.g. Grub is installed there!)
Check what device your USB media is assigned - here we will assume it is /dev/sdb. Delete all partitions, create a new one taking up all the space, set type to NTFS (7), and remember to set it bootable:
# cfdisk /dev/sdb or fdisk /dev/sdb (partition type 7, and bootable flag)
Create an NTFS filesystem:
# mkfs.ntfs -f /dev/sdb1
Write Windows 7 MBR on the USB stick (also works for windows 8), multiple options here:
# ms-sys -7 /dev/sdb- or (e.g. on newer Ubuntu installs)
sudo lilo -M /dev/sdb mbr (info)
- or (if syslinux is installed), you can run
sudo dd if=/usr/lib/syslinux/mbr/mbr.bin of=/dev/sdb
Mount ISO and USB media:
# mount -o loop win7.iso /mnt/iso
# mount /dev/sdb1 /mnt/usb
Copy over all files:
# cp -r /mnt/iso/* /mnt/usb/ ...or use the standard GUI file-browser of your system
Call sync to make sure all files are written.
Open gparted, select the USB drive, right-click on the file system, then click on "Manage Flags". Check the boot checkbox, then close.
...and you're done.
After all that, you probably want to back up your USB media for further installations and get rid of the ISO file... Just use dd:
# dd if=/dev/sdb of=win7.img
Note, this copies the whole device! — which is usually (much) bigger than the files copied to it. So instead I propose
# dd count=[(size of the ISO file in MB plus some extra MB for boot block) divided by default dd blocksize] if=/dev/sdb of=win7.img
Thus for example with 8 M extra bytes:
# dd count=$(((`stat -c '%s' win7.iso` + 8*1024*1024) / 512)) if=/dev/sdb of=win7.img status=progress
As always, double check the device names very carefully when working with dd.
The method creating a bootable USB presented above works also with Win10 installer iso. I tried it running Ubuntu 16.04 copying Win10_1703_SingleLang_English_x64.iso (size 4,241,291,264 bytes) onto an 8 GB USB-stick — in non-UEFI [non-secure] boot only. After execution dd reports:
8300156+0 records in
8300156+0 records out
4249679872 bytes (4.2 GB, 4.0 GiB) copied, 412.807 s, 10.3 MB/s
Reverse if/of next time you want to put the Windows 7 installer onto USB.
Best Answer
Take a look at sdparm. It looks like there is an official OpenWRT package, which you should be able to install via opkg/ipkg.
Try this: