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OS: Raspberry Buster Lite

Board: Raspberry Pi 4

I have been playing with dhcpcd.conf for the last few days. I am trying to change the network settings from within a C++ program. The program reads the new network settings from a .txt file and applies them correctly over (overwriting) dhcpcd.conf and wpa_supplicant.conf, respectively. And then it does system("ip link set eth0 down && ip link set eth0 up && ip link set wlan0 down && ip link set wlan0 up");.

The thing is that the interfaces go down and then up but they don't have any IP assigned to them.

This is the current content of dhcpcd.conf:

interface wlan0
hostname PiWiFi
clientid PiWiFi
static ip_address=192.168.1.120/24
static routers=192.168.1.1
static domain_name_servers=8.8.8.8
interface eth0
noipv4
noipv6

with wpa_supplicant.conf:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="MySSID"
psk="Password1234"
}

I have also tried this dhcpcd.conf:

interface wlan0
noipv4
noipv6
interface eth0
hostname PiEth
clientid PiEth
static ip_address=192.168.1.20/24
static routers=192.168.1.1
static domain_name_servers=8.8.8.8

with wpa_supplicant.conf:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

eth0 receives an IP Address ! wlan0 does not.

Also, I have tried disabling the service that runs the C++ program, rebooting the Raspberry and then manually changing dhcpcd.conf and wpa_supplicant.conf and it is the same story. wlan0 won't work.

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1 Answer 1

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3

To configure the interfaces with ip addresses the dhcpcd.service is used. That's the reason why you set them in /etc/dhcpcd.conf. It seems that only setting the interfaces down and up with ip does not trigger dhcpcd to reconfigure the interfaces. Try to use:

system("systemctl daemon-reload && systemctl restart dhcpcd.service")

of course with root rights.

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5
  • But ip link set eth0 down && ip link set eth0 works. So, dhcpcd reconfigures the eth0 interface. Why isn't wlan0 working ?
    – bleah1
    Commented Sep 24, 2019 at 8:07
  • Also, systemctl daemon-reload && systemctl restart dhcpcd.service with root rights had no effect. wlan0 still doesnt' have any IP
    – bleah1
    Commented Sep 24, 2019 at 8:17
  • I've went into raspi-config and set a ssid and password and, as expected, wlan0 was assigned a dhcp IP. Then I've went into /etc/dhcpcd.conf and /etc/wpa_supplicant/wpa_supplicant.conf files and the only lines that were added were network={ ssid="MySSID" psk="Password1234" }
    – bleah1
    Commented Sep 24, 2019 at 8:25
  • @bleah1 If everything works on the command line then the problem must be your C++ program. I can't say much about it because I don't know it. Maybe you don't match the correct environment to execute system commands in the invoked shell?
    – Ingo
    Commented Sep 24, 2019 at 9:33
  • I've ended up adding country=" and the country code to wpa_supplicant.conf` and also using system("systemctl daemon-reload && systemctl restart dhcpcd.service") whenever I change the network settings and it works nicely. I don't know which fixed it.
    – bleah1
    Commented Sep 27, 2019 at 11:47

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