We are going to download a Live image from Debian web site, then save it in an USB storage, and boot our computer from it.
This image allows us to simply run a live system or install a new one.
Download Live Image
Download the image from here:
http://cdimage.debian.org/debian-cd/current-live/
For amd64 architecture:
http://cdimage.debian.org/debian-cd/current-live/amd64/iso-hybrid/
$ wget http://cdimage.debian.org/debian-cd/current-live/amd64/iso-hybrid/debian-live-8.3.0-amd64-standard.iso
Length: 436207616 (416M) [application/x-iso9660-image]
Saving to: ‘debian-live-8.3.0-amd64-standard.iso’
debian-live-8.3.0-a 100%[===================>] 416.00M 8.34MB/s in 38s
2016-02-21 11:54:31 (10.8 MB/s) - ‘debian-live-8.3.0-amd64-standard.iso’ saved [436207616/436207616]
Write to USB storage device
https://www.debian.org/CD/faq/#write-usb
NOTE: Take care you select the right device to write to.
dd if=<input file> of=<output file> bs=4M; sync
E.g:
$ dd if='debian-live-8.3.0-amd64-standard.iso' of=/dev/sdb bs=4M; sync
sync ensures all writes are flushed out to disk.
bs=4M is for effiency (instead of 512 default)
104+0 records in
104+0 records out
436207616 bytes (436 MB) copied, 113.028 s, 3.9 MB/s
Then you can extract the usb or reboot your computer and select boot from USB device.
Password
Live system does not log on automatically. It asks for user and password:
user: user
pass: live
REFERENCE
https://www.debian.org/CD/live/