Issue
I want to change the static IP address for interface eth0 on my raspberry pi 4 from a web page. I am running buster lite 4.19 with no desktop. From what I understand, I need to modify the "static ip_address=" line in the /etc/dhcpcd.conf file to make the change permanent.
I can execute the following command and it works fine until I restart the controller.
ifconfig eth0 192.168.1.10 netmask 255.255.255.0
I found this link which works great from the command line. Using sed to change ip addresses in dhcpcd.conf file
I attempted to use the exec() command to execute the commands from the php script. The read works fine but the sed operation does not write anything. I am assuming a permissions issue but not sure how to overcome this. I am using the following commands in my code.
$newIPcidr = "192.168.1.10/24";
$cmd = "cat /etc/dhcpcd.conf | grep -e '^static ip_address=' | cut -d= -f2";
$curIP = exec($cmd);
$cmd = "sudo sed -i -e \"s@^static ip_address=" . $curIP . "\b@static ip_address=" . $newIPcidr . "@g\" /etc/dhcpcd.conf";
$output = exec($cmd);
Is there a better way to do this?
Thanks in advance for any help on this!
Solution
I think your problem is the generic one of executing a command as root when you are not root.
There are several ways around this:
1/. write a specific script or binary that executes as root.
2/. use sudo and ensure that the pi web identity (www-data) has an entry in the /etc/sudoers file to enable it to execute the command you specify as root, without using a password
3/. change the permissions on the file you want to e.g. group write and make its group www-data. Hmm. I see that mine is netdev. possibly safer then to give it 666 permissions so that its world writable, and leave the group the same.
I think for a quick hack in a protected environment the latter might be easiest. e.g sudo chmod 666 /etc/dhcpcd.conf and see if that works.
2/. is OK for reasonably secure environments.
I've used 1/. when I want all users to be able to execute something root-ish
Answered By - Leo Smith
