Create bootable USB on Linux or OS x command line

[rick]

To create a bootable image on a USB ‘stick’ aka ‘thumb drive’ ‘flash drive’ in linux or OS x we use the ‘dd’ command.

In this case, we’ll write the latest (as of this writeup) Debian Image , which happens to be 8.5.0 amd64

I generally try to use the torrent, taking in consideration the server/ bandwidth costs involved with free and open software.

Download the image you wish to use. Many times the image you use, will depend on what size USB device you have available. Or obviously what you wish to accomplish.

In this case I’m using a USB card reader, with a 32 GB Micro SD card

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You’ll need to know what USB device name to use. An easy way to view what devices are currently mounted would be to use:

lsblk

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There are many options, or flags if you need them. From the man pages:

       -a, --all
              Also list empty devices.  (By default they are skipped.)

       -b, --bytes
              Print the SIZE column in bytes rather than in a human-readable
              format.

       -D, --discard
              Print information about the discarding capabilities (TRIM,
              UNMAP) for each device.

       -d, --nodeps
              Do not print holder devices or slaves.  For example, lsblk
              --nodeps /dev/sda prints information about the sda device
              only.

       -e, --exclude list
              Exclude the devices specified by the comma-separated list of
              major device numbers.  Note that RAM disks (major=1) are
              excluded by default.  The filter is applied to the top-level
              devices only.

       -f, --fs
              Output info about filesystems.  This option is equivalent to
              -o NAME,FSTYPE,LABEL,UUID,MOUNTPOINT.  The authoritative
              information about filesystems and raids is provided by the
              blkid(8) command.

       -h, --help
              Display help text and exit.

       -I, --include list
              Include devices specified by the comma-separated list of major
              device numbers.  The filter is applied to the top-level
              devices only.

       -i, --ascii
              Use ASCII characters for tree formatting.

       -J, --json
              Use JSON output format.

       -l, --list
              Produce output in the form of a list.

       -m, --perms
              Output info about device owner, group and mode.  This option
              is equivalent to -o NAME,SIZE,OWNER,GROUP,MODE.

       -n, --noheadings
              Do not print a header line.

       -o, --output list
              Specify which output columns to print.  Use --help to get a
              list of all supported columns.

              The default list of columns may be extended if list is
              specified in the format +list (e.g. lsblk -o +UUID).

       -O, --output-all
              Output all available columns.

       -P, --pairs
              Produce output in the form of key="value" pairs.  All
              potentially unsafe characters are hex-escaped (\x<code>).

       -p, --paths
              Print full device paths.

       -r, --raw
              Produce output in raw format.  All potentially unsafe
              characters are hex-escaped (\x<code>) in the NAME, KNAME,
              LABEL, PARTLABEL and MOUNTPOINT columns.

       -S, --scsi
              Output info about SCSI devices only.  All partitions, slaves
              and holder devices are ignored.

       -s, --inverse
              Print dependencies in inverse order.

       -t, --topology
              Output info about block-device topology.  This option is
              equivalent to -o NAME,ALIGNMENT,MIN-IO,OPT-IO,PHY-SEC,LOG-
              SEC,ROTA,SCHED,RQ-SIZE,RA,WSAME.

       -V, --version
              Display version information and exit.

       -x, --sort column
              Sort output lines by column.

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In this case, the system spits out the following disks:

NAME                        MAJ:MIN RM   SIZE RO TYPE   MOUNTPOINT
sda                           8:0    0 465.8G  0 disk   
└─isw_ccheigfjba_Volume0    254:0    0 931.5G  0 dmraid 
  ├─isw_ccheigfjba_Volume01 254:1    0 893.8G  0 dmraid /
  └─isw_ccheigfjba_Volume05 254:3    0  37.7G  0 dmraid 
sdb                           8:16   0 465.8G  0 disk   
└─isw_ccheigfjba_Volume0    254:0    0 931.5G  0 dmraid 
  ├─isw_ccheigfjba_Volume01 254:1    0 893.8G  0 dmraid /
  └─isw_ccheigfjba_Volume05 254:3    0  37.7G  0 dmraid 
sdc                           8:32   1   1.9G  0 disk   
├─sdc1                        8:33   1   925M  0 part   
└─sdc2                        8:34   1  86.1M  0 part

We can see three devices on this system shown by ‘sda’ ‘sdb’ and ‘sdc’, where sda and sdb are each 500GB drives in a raid array. And sdc is the USB device we’ll use.

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These naming conventions will not always be the case, depending on operating system. sdc will not always be your USB device.

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It’s very important to insure you are writing to the correct disk, as well as not trying to write to a partition on the desired target disk. As in:

sdc                           8:32   1   1.9G  0 disk   
├─sdc1                        8:33   1   925M  0 part   
└─sdc2                        8:34   1  86.1M  0 part

Where in the above example, we see ‘sdc’ as the disk, and two partitions called ‘sdc1’ and ‘sdc2’

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You could go about formatting the disk at this point, however the commands we will use in this example will simply ignore and over write any and all partitions, erasing any and all data on the target device. Effectively destroying anything currently on the device.

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Once the image, or ISO is downloaded to your local machine, navigate to the directory which your downloads reside (generally the users ‘Download’ directory).

Of course it is not required to move to the directory where the image is, at that point you’ll need to type the path, I say go to the Downloads directory for easy of use and simplify the command.

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In this case the image name is: debian-8.5.0-amd64-DVD-1.iso

The disk is: sdc

So the command to write the image ‘debian-8.5.0-amd64-DVD-1.iso’ To disk ‘sdc’

You may need to unmount the device before this will work

umount /dev/sdc 

You would then run the following command:

sudo dd if=debian-8.5.0-amd64-DVD-1.iso of=/dev/sdc bs=1M

You’ll of course be requested to type in your sudo password, or at least you should not be running as root to begin with.

The write will commence, and depending on the machine capabilities and the size of the image being written, will dictate the speed at which the procedure takes.

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There is no progress bar with this command, so sit back, or get on with another task. This could take quite some time.

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Once the image is written to the USB device and completed, the output will look something to this effect:

3808+0 records in
3808+0 records out
3992977408 bytes (4.0 GB) copied, 288.986 s, 13.8 MB/s

We can see here, that the USB device is now partitioned and the ISO is available.

sdc                           8:32   1  29.7G  0 disk   
├─sdc1                        8:33   1   3.7G  0 part   /media/rick/Debian 8.5.0 amd64 1
└─sdc2                        8:34   1   416K  0 part

There is quite a lot of discussion as to which block size to write, or as seen in the above command ‘bs=1M’ , I have used 5M, however much faster, I’ve had instances where {something @ somewhere} went sour and left me with a useless image. Possibly due to incorrect writes, that is however for another discussion.