Script to create users in an Asus router (OpenWRT) to login via SSH for instance

create_user.sh

#!/bin/sh
echo -e "\nUsage: create_user.sh <username> <password>"
USERNAME=$1
PASSWORD=$2
echo "Creating user ${USERNAME}"

if [ ! -d "/home/${USERNAME}" ] 
then    
    echo "Directory /home/${USERNAME} does not exist. Let's continue normally."
    mkdir /home/${USERNAME}
    chown ${USERNAME} /home/${USERNAME}
    echo "${USERNAME}:x:200:200:${USERNAME}:/home/${USERNAME}:/bin/sh" >> /jffs/configs/passwd.add
    echo "${USERNAME}:@ZZZZ@:0:0:99999:7:0:0:" >> /jffs/configs/shadow.add
    echo "${USERNAME}:x:200:" >> /jffs/configs/group.add
    echo "${USERNAME}:*:200:" >> /jffs/configs/gshadow.add
    echo "${USERNAME}:x:200:200:${USERNAME}:/home/${USERNAME}/:/bin/sh" >> /etc/passwd
    echo "mkdir /home/${USERNAME}" >> /jffs/configs/users_to_add_on_every_reboot.sh
    echo "chown ${USERNAME} /home/${USERNAME}" >> /jffs/configs/users_to_add_on_every_reboot.sh
else 
    echo "Directory /home/${USERNAME} already exists. Let's only update the password."
    sed -i.bak "/${USERNAME}:/d" /jffs/configs/shadow.add
    echo "${USERNAME}:@ZZZZ@:0:0:99999:7:0:0:" >> /jffs/configs/shadow.add
fi

echo "${USERNAME}:$PASSWORD" | sudo chpasswd
ENCRYPTED_PASSWORD=`cat /etc/passwd | grep -Po "${USERNAME}:\K(.*)(?=:200:200:)" | head -n 1`
#echo "New encrypted password $ENCRYPTED_PASSWORD"
sed -i "s/${USERNAME}:@ZZZZ@/${USERNAME}:${ENCRYPTED_PASSWORD}/g" /jffs/configs/shadow.add
if [ $? -eq 0 ]; then
    echo -e "All done\n"
else
    echo -e "- IMPORTANT ERROR. PLEASE READ - User action is required: The last command (sed) failed since it is likely that the generated encrypted password has a '/'. You must either a) re-run this script (the time-based seed will create a different password), or b) copy the encrypted password from /etc/passwd and paste it into /jffs/configs/shadow.add replacing @ZZZZ@\n"
fi

how to fix

admin@RT-AC86U-BA98:/tmp/home/root# sudo
sudo: unknown user: root
sudo: unable to initialize policy plugin

Enabling SUDO (root)

echo 'root:x:0:0:root:/root:/bin/sh' >> /jffs/configs/passwd.add
opkg install sudo
chmod u+w /opt/etc/sudoers

Now, we need to paste a text line inside sudoers file. So, first:

vi /opt/etc/sudoers

Now, paste this line inside User alias specification section

admin    ALL=(ALL:ALL) ALL

Now you can run a command with sudo

Great, works now. Thanks a million!