Installing operating system images on Linux

Etcher is typically the easiest option for most users to write images to SD cards, so it is a good place to start. If you're looking for more advanced options on Linux, you can use the standard command line tools below.

Note: use of the dd tool can overwrite any partition of your machine. If you specify the wrong device in the instructions below, you could delete your primary Linux partition. Please be careful.

Discovering the SD card mountpoint and unmounting it

  • Run df -h to see which devices are currently mounted.

  • If your computer has a slot for SD cards, insert the card. If not, insert the card into an SD card reader, then connect the reader to your computer.

  • Run df -h again. The new device that has appeared is your SD card. If no device appears, then your system is not automounting devices. In this case, you will need to search for the device name using another method. The dmesg | tail command will display the most recent system messages, which should contain information on the naming of the SD card device. The naming of the device will follow the format described in the next paragraph. Note that if the SD card was not automounted, you do not need to unmount later.

  • The left column of the results from df -h command gives the device name of your SD card. It will be listed as something like /dev/mmcblk0p1 or /dev/sdX1, where X is a lower case letter indicating the device. The last part (p1 or 1 respectively) is the partition number. You want to write to the whole SD card, not just one partition. You therefore need to remove that section from the name. You should see something like /dev/mmcblk0 or /dev/sdX as the device name for the whole SD card. Note that the SD card can show up more than once in the output of df. It will do this if you have previously written a Raspberry Pi image to this SD card, because the Raspberry Pi SD images have more than one partition.

  • Now you have noted the device name, you need to unmount it so that files can't be read or written to the SD card while you are copying over the SD image.

  • Run umount /dev/sdX1, replacing sdX1 with whatever your SD card's device name is, including the partition number.

  • If your SD card shows up more than once in the output of df, this shows that the card has multiple partitions. You should unmount all of these partitions.

Copying the image to the SD card

  • In a terminal window, write the image to the card with the command below, making sure you replace the input file if= argument with the path to your .img file, and the /dev/sdX in the output file of= argument with the correct device name. This is very important, as you will lose all the data on the hard drive if you provide the wrong device name. Make sure the device name is the name of the whole SD card as described above, not just a partition. For example: sdd, not sdds1 or sddp1, and mmcblk0, not mmcblk0p1.

    dd bs=4M if=2017-09-07-raspbian-stretch.img of=/dev/sdX conv=fsync
  • Please note that block size set to 4M will work most of the time. If not, try 1M, although this will take considerably longer.

  • Also note that if you are not logged in as root you will need to prefix this with sudo.

Copying a zipped image to the SD card

In Linux it is possible to combine the unzip and SD copying process into one command, which avoids any issues that might occur when the unzipped image is larger than 4GB. This can happen on certain filesystems that do not support files larger than 4GB (e.g. FAT), although it should be noted that most Linux installations do not use FAT and therefore do not have this limitation.

The following command unzips the zip file (replace 2017-09-07-raspbian-stretch.zip with the appropriate zip filename), and pipes the output directly to the dd command. This in turn copies it to the SD card, as described in the previous section.

unzip -p 2017-09-07-raspbian-stretch.zip | sudo dd of=/dev/sdX bs=4M conv=fsync

Checking the image copy progress

  • By default, the dd command does not give any information about its progress, so it may appear to have frozen. It can take more than five minutes to finish writing to the card. If your card reader has an LED, it may blink during the write process.

  • To see the progress of the copy operation, you can run the dd command with the status option.
    dd bs=4M if=2017-09-07-raspbian-stretch.img of=/dev/sdX status=progress conv=fsync
  • If you are using an older version of dd, the status option may not be available. You may be able to use the dcfldd command instead, which will give a progress report showing how much has been written. Another method is to send a USR1 signal to dd, which will let it print status information. Find out the PID of dd by using pgrep -l dd or ps a | grep dd. Then use kill -USR1 PID to send the USR1 signal to dd.

Checking whether the image was correctly written to the SD card

  • After dd has finished copying, you can check what has been written to the SD card by dd-ing from the card back to another image on your hard disk; truncating the new image to the same size as the original; and then running diff (or md5sum) on those two images.

  • If the SD card is bigger than the original image size, dd will make a copy of the whole card. We must therefore truncate the new image to the size of the original image. Make sure you replace the input file if= argument with the correct device name. diff should report that the files are identical.

    dd bs=4M if=/dev/sdX of=from-sd-card.img
    truncate --reference 2017-09-07-raspbian-stretch.img from-sd-card.img
    diff -s from-sd-card.img 2017-09-07-raspbian-stretch.img
  • Run sync. This will ensure the write cache is flushed and that it is safe to unmount your SD card.

  • Remove the SD card from the card reader.