Change static IP address from PHP script on raspbian

Question

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!

Leo Smith · Accepted Answer · 2020-06-24 06:26:21Z

1

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 Jun 24, 2020 at 6:26

Leo Smith

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2 Comments

ChrisE Over a year ago

Thank you Leo, I will give this a try.

ChrisE Over a year ago

I decided to use option 2 and change group to www-data and add that user with sed access only to sudoers. Works great! I am not an expert in apache or linux security so what potential security issues did I just create for myself?

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