Setting up RPi

This write up allow you to to set up your Raspberry Pi for ssh We acheive this by manually activating sshd in Pi's root partition. Followed by writing a systemd service file which activates the WiFi. In this case, I will be connecting my Pi to my smartphone's mobile hotspot and my pc to the hotspot as well. And then ssh into the Pi.

Mount the SD card

Mount the root partition of the SD card.

Some linux system automatically mounts them, like in my case I use Gnome. You can check where it has mounted by

df -h

Export that directory as ROOT variable.

export ROOT directory_where_root_partition_is_mounted

If you system hasn't mounted automatically, follow the instructions below.

Connect the SD card to a linux PC, then do fdisk -l, find the device of root partition. Example: My PC showed these results.

Disk /dev/sda: 14.9 GiB, 15931539456 bytes, 31116288 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: 0xa8431c25

Device     Boot  Start      End  Sectors  Size Id Type
/dev/sda1         8192   137215   129024   63M  c W95 FAT32 (LBA)
/dev/sda2       137216 31116287 30979072 14.8G 83 Linux

We need to mount /dev/sda2. Note that I figure it out by the size and type parameters.

Then mount the root parttiton. Export to ROOT

mkdir root
sudo mount /dev/sda2 root
cd root
export ROOT $(pwd)

Setting up sshd manually by systemd service files.

sshd to run on startup is disabled by default. We need to find the sshd.service file. From my search, I found it on var/lib/systemd/deb-systemd-helper-enabled/sshd.service Then link that sshd.service file to $ROOT/etc/systemd/system/sshd.service

ln -s $ROOT/var/lib/systemd/deb-systemd-helper-enabled/sshd.service $ROOT/etc/systemd/system/sshd.service

Setting Up WiFi

Go to $ROOT/home/pi/, create 2 files.

touch start_wifi start_wifi.service

Write the following in the start_wifi.service, usenano start_wifi.service

[Unit]
Description=Connect Rpi to my Hotspot

[Service]
Type=oneshot
ExecStart=/home/pi/start_wifi

[Install]
WantedBy=multi-user.target

Save it in nano by ctrl-x

And this in start_wifi file

wpa_supplicant -D -P/home/pi/wpa.pid -iwlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf

Save it.

We need to active this start up script by adding it to the systemd.

ln -s $ROOT/home/pi/start_wifi.service $ROOT/etc/systemd/system/start_wifi.service
ln -s $ROOT/home/pi/start_wifi.service $ROOT/etc/systemd/system/multi-user.target.wants/start_wifi.service

Now, we need to edit the $ROOT/etc/wpa_supplicant/wpa_supplicant.conf adding our mobile hotspot's details. Open the same using nano and add the following lines.

network={
    ssid="HOTSPOT NAME"
    psk="HOTSPOT PASSWD"
}

This should work, fingers crossed

Save it!

We are now done with editing the necessary files, now un mount by

umount $ROOT

Hook up the Pi

Insert the SD card on Pi, start your phone's hotspot. Boot up the Pi.

If everything was done right, your phone must have indicated a new device connected. Connect your PC to the same hotspot If your phone doesn't show up the ip use nmap tool to find it out.

nmap 192.168.43.*

Note: I assumed the fist 3 octets of ip by checking my PC's ip address.

After discovering ip, ssh into it by

ssh pi@<IP_ADDRESS>

Where <IP_ADDRESS> is Pi's ip address.

You will be prompted for passwd, enter that, Voila! You are in Pi!

Happy hacking :D