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--- doc:appunti:hardware:raspberrypi_wpa_supplicant_problem [2024/11/15 10:27] – [dhcpcd process dies without configuring wlan0] niccolo
+++ doc:appunti:hardware:raspberrypi_wpa_supplicant_problem [2024/11/17 16:55] (current) – [dhcpcd process dies without configuring wlan0] niccolo
@@ Line 63: / Line 63: @@
 ===== dhcpcd process dies without configuring wlan0 =====
-This is a similar problem encountered on a **Raspberry Pi Model B Rev 2** running Raspbian GNU/Linux 11 Bullseye, the **wlan0** interface is an USB dongle **Realtek RTL8188CUS**, the **eth0** interface is not used and **dhcpcd** is instructed to ignore it (via the ''denyinterfaces eth0'' option in **/etc/dhcpcd.conf**).
+This is a similar problem encountered on a **Raspberry Pi Model B Rev 2** running Raspbian GNU/Linux 11 Bullseye. The **wlan0** interface is an USB dongle **Realtek RTL8188CUS**, the **eth0** interface is not used and **dhcpcd** is instructed to ignore it (via the ''denyinterfaces eth0'' option in **/etc/dhcpcd.conf**).
-At first I decided to **disable** the Systemd **wpa_supplicant.service** and let **dhcpcd** to manage the interface starting wpa_supplicant on its own, as seen above. Suddendly the system started to have random problems on bootstrap: sometimes the host resulted having the wpa_supplicant process (lanched by dhcpcd) running, but **the dhcpcd process itself was die** and did not configured the IP address on the wlan0 interface.
+At first I decided to **disable** the Systemd **wpa_supplicant.service** and let **dhcpcd** to manage the interface starting wpa_supplicant on its own, as seen above. Suddendly the system started to have random problems on bootstrap: sometimes the host resulted having the wpa_supplicant process running (lanched by dhcpcd), but **the dhcpcd process itself was die** and did not configured the IP address on the wlan0 interface.
 To trace the problem I had to enable the debugging option of dhcpcd, adding the **%%-d%%** parameter in **/etc/systemd/system/dhcpcd.service.d/wait.conf**; the log can be read with **journalctl -b -t dhcpcd**.
@@ Line 112: / Line 112: @@
 It results that wlan0 gets a sqeuence of ''wlan0: carrier acquired'' and ''wlan0: carrier lost'', after that the fatal error **main: eloop_start: Invalid argument** kills dhcpcd. Maybe this problem is triggered by the autoconfiguration of IPv6.
-I solved the problem by letting Systemd to start wpa_supplicant on the specific wlan0 interface. This is achieved renaming the wpa_supplicant.conf file and enabling the service:
+I solved the problem by letting Systemd to start wpa_supplicant on the specific wlan0 interface. This is achieved renaming the wpa_supplicant.conf file and enabling only the interface-specific version service:
 <code>
 mv /etc/wpa_supplicant/wpa_supplicant.conf /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
 systemctl enable wpa_supplicant@wlan0.service
+systemctl disable wpa_supplicant.service
 </code>
@@ Line 134: / Line 135: @@
 Nevertehless dhcpcd is informed by udev when the wlan0 interface is activated and then it can configure it using DHCP.
+**NOTICE**: The default systemd configuration shipped with **Raspbian 11 Bullseye** does not ensure that the **wpa_supplicant@..service** is started before **dhcpcd.service**, thus ensuring that the above startup sequence is respected. You can generate the SVG graphic detailing which system services have been started at what time using the command:
+<code>
+systemd-analyze plot > services-start-graph.svg
+</code>
+Indeed you can see that **dhcpcd.service** becomes active after the **wpa_supplicant@wlan0.service**, but nothing is ensuring this behaviour. We should actually customize the dhcpcd.service unit adding an **After=wpa_supplicant@..service** option. For this purpose we use the command **systemctl edit**:
+<code>
+systemctl edit dhcpcd.service
+</code>
+this will launch an editor to create the file **/etc/systemd/system/dhcpcd.service.d/override.conf**; this is a drop-in snippet to extend or override the definition of the unit. Here we write:
+<file>
+[Unit]
+After=wpa_supplicant@..service
+</file>
+The systemd daemon will be automatically reloaded, se we can reboot.
 ===== Web References =====
   * [[https://www.raspberrypi.org/forums/viewtopic.php?t=191061|Raspbian Stretch: Wifi not starting on boot]]