How do I setup wifi on without being able to login?

Question

I have a laptop, a power cable, an sd card, and a Pi3 (wifi built in).

I'm trying to ssh in but first I need to setup the wifi. Where on the boot partition can I setup wifi (cmdline.txt?) with a hostname and a password?

Answer 1

Since you have not mentioned some details I think are relevant to the answer such as

• what OS you are running on PI (which supports many)
• OS running on the remote machine from which you want to ssh in from,

I will assume the following

PI: raspbian/jessie which the latest as of this writing

Remote: some flavor of linux

This is how I'd go about setting up the customized image from the remote machine

• download the official raspbian OS image file which should come bundled with the required drivers, firmware compatible with the included kernel.

  https://www.raspberrypi.org/downloads/raspbian/

• unzip the archive to extract img file. lets call this image file jessie.img for this post

• the jessie.img file should contain 2 partitions - one for boot (FAT32) and for the rest (EXT4)

• use fdisk to find out the file offsets of the partitions.

• we are interested in the offset of the EXT4 partition which contains the root file system
• here is a sample o/p

---

fdisk -l ./jessie.img

Disk ./jessie.img: 4.1 GiB, 4348444672 bytes, 8493056 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd94ffdb3

Device        Boot  Start     End Sectors Size Id Type
./jessie.img1        8192  137215  129024  63M  c W95 FAT32 (LBA)
./jessie.img2      137216 8493055 8355840   4G 83 Linux

---

• here jessie.img2 starts at block 137216 with each block 512 bytes long. so the total offset is the product of the two = 70254592 bytes

• next step is mount the jessie.img2 as read/write so that we can edit the /etc/network/interfaces

• make a temporary mount point

---

mkdir ~/mntpt

---

• mount the partition

---

sudo mount -o loop,rw,offset=70254592 jessie.img ./mntpt

---

• change directory to the mount point and verify the required folder exist

---

cd ./mntpt
ls

bin  boot  dev  etc  home  lib  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

---

• change directory to etc

---

cd ./etc

---

• verify the interfaces file is setup properly

---

less ./network/interfaces

# interfaces(5) file used by ifup(8) and ifdown(8)

# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'

# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto lo
iface lo inet loopback

iface eth0 inet manual

allow-hotplug wlan0
iface wlan0 inet manual
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan1
iface wlan1 inet manual
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

---

• edit the /etc/wpa_supplicant/wpa_supplicant.conf file and add the new lines, customize to match your setup, save and exit

---

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

network={
ssid="YOUR_NETWORK_NAME"
psk="YOUR_NETWORK_PASSWORD"
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP
auth_alg=OPEN
}

---

• go back two folders from etc

---

cd ..
cd ..

---

• unmount the image

---

sudo unmount ./mntpt

---

• now the image should be ready to be written out to the disk and booted up

References

• https://major.io/2010/12/14/mounting-a-raw-partition-file-made-with-dd-or-dd_rescue-in-linux/
• http://weworkweplay.com/play/automatically-connect-a-raspberry-pi-to-a-wifi-network/
• https://askubuntu.com/questions/445979/mount-sd-card-image-created-using-dd

Notes

• there are number of other tools such as parted which also provides the same information as fdisk

• kpartx makes it bit easier to mount the individual partitions

• Since this technique requires some unix/linux tools, it might be harder to do the same from a windows machine. a mingw / cgywin setup might work but i have not tried them

• if you spot any mistakes or encounter any error messages along the way, please leave a comment and I will try to address them the best I can