Why dhcpcd.service failed for auto matically alllow ip address

Question

I using Raspbery pi zero w.

my dhcpcd.service always fail, I do not know the reason: my linux is:

PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"
NAME="Raspbian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

My dhcpcd.service status:

root@raspberrypi:/var/lib/dhcpcd5# systemctl status dhcpcd.service
● dhcpcd.service - dhcpcd on all interfaces
   Loaded: loaded (/lib/systemd/system/dhcpcd.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2020-10-08 01:12:21 BST; 5 days ago
  Process: 284 ExecStart=/usr/lib/dhcpcd5/dhcpcd -q -b (code=exited, status=6)  #####dhcpcd service failed.

Oct 08 01:12:18 raspberrypi systemd[1]: Starting dhcpcd on all interfaces...
Oct 08 01:12:18 raspberrypi dhcpcd[284]: Not running dhcpcd because /etc/network/interfaces
Oct 08 01:12:18 raspberrypi dhcpcd[284]: defines some interfaces that will use a
Oct 08 01:12:18 raspberrypi dhcpcd[284]: DHCP client or static address
Oct 08 01:12:21 raspberrypi systemd[1]: dhcpcd.service: Control process exited, code=exited, status=
Oct 08 01:12:21 raspberrypi systemd[1]: dhcpcd.service: Failed with result 'exit-code'.
Oct 08 01:12:21 raspberrypi systemd[1]: Failed to start dhcpcd on all interfaces.

My /etc/network/interfaces

iface lo inet loopback

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
      pre-up wpa_supplicant -B -Dwext -i wlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf
      post-down killall -q wpa_supplicant

auto usb0
allow-hotplug usb0
iface usb0 inet auto

I do not change dhcpcd.conf

# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.

# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel

# Inform the DHCP server of our hostname for DDNS.
hostname

# Use the hardware address of the interface for the Client ID.
clientid
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# Some non-RFC compliant DHCP servers do not reply with this set.
# In this case, comment out duid and enable clientid above.
#duid

# Persist interface configuration when dhcpcd exits.
persistent

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search, host_name
option classless_static_routes
# Respect the network MTU. This is applied to DHCP routes.
option interface_mtu

# Most distributions have NTP support.
#option ntp_servers

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# Generate SLAAC address using the Hardware Address of the interface
#slaac hwaddr
# OR generate Stable Private IPv6 Addresses based from the DUID
slaac private

# Example static IP configuration:
#interface eth0
#static ip_address=192.168.0.10/24
#static ip6_address=fd51:42f8:caae:d92e::ff/64
#static routers=192.168.0.1
#static domain_name_servers=192.168.0.1 8.8.8.8 fd51:42f8:caae:d92e::1

# It is possible to fall back to a static IP if DHCP fails:
# define static profile
#profile static_eth0
#static ip_address=192.168.1.23/24
#static routers=192.168.1.1
#static domain_name_servers=192.168.1.1

# fallback to static profile on eth0
#interface eth0

It seems it execute

dhcpcd -q -b

and then fails. I can execute this command manually, but when I try to run service it failed.

root@raspberrypi:/etc# sysctemctl restart dhcpcd.service
-bash: sysctemctl: command not found
root@raspberrypi:/etc# systemctl restart dhcpcd.service
Job for dhcpcd.service failed because the control process exited with error code.
See "systemctl status dhcpcd.service" and "journalctl -xe" for details.
root@raspberrypi:/etc# dhcpcd
dev: loaded udev
wlan0: connected to Access Point `Accept'
DUID 00:01:00:01:26:d1:12:f4:b8:27:eb:e7:9a:7d
usb0: IAID 07:f0:38:78
wlan0: IAID eb:e7:9a:7d
wlan0: soliciting an IPv6 router
usb0: soliciting an IPv6 router
wlan0: rebinding lease of 10.125.132.171
wlan0: leased 10.125.132.171 for 10800 seconds
wlan0: adding route to 10.125.128.0/20
wlan0: adding default route via 10.125.128.1
forked to background, child pid 2066

You can see the dhcpcd can run manually but when it in service it failed.

root@raspberrypi:/etc# journalctl -xe
Oct 13 01:49:43 raspberrypi systemd[1]: Starting dhcpcd on all interfaces...
-- Subject: A start job for unit dhcpcd.service has begun execution
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- A start job for unit dhcpcd.service has begun execution.
--
-- The job identifier is 1107.
Oct 13 01:49:43 raspberrypi dhcpcd[2082]: Not running dhcpcd because /etc/network/interfaces
Oct 13 01:49:43 raspberrypi dhcpcd[2082]: defines some interfaces that will use a
Oct 13 01:49:43 raspberrypi dhcpcd[2082]: DHCP client or static address
Oct 13 01:49:43 raspberrypi systemd[1]: dhcpcd.service: Control process exited, code=exited, status=
-- Subject: Unit process exited
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- An ExecStart= process belonging to unit dhcpcd.service has exited.
--
-- The process' exit code is 'exited' and its exit status is 6.
Oct 13 01:49:43 raspberrypi systemd[1]: dhcpcd.service: Failed with result 'exit-code'.
-- Subject: Unit failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- The unit dhcpcd.service has entered the 'failed' state with result 'exit-code'.
Oct 13 01:49:43 raspberrypi systemd[1]: Failed to start dhcpcd on all interfaces.
-- Subject: A start job for unit dhcpcd.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- A start job for unit dhcpcd.service has finished with a failure.
--
-- The job identifier is 1107 and the job result is failed.
Oct 13 01:49:46 raspberrypi dhcpcd[2084]: dhcpcd not running

and the service file is:

root@raspberrypi:/etc/systemd/system# ls
[email protected]                      display-manager.service      rc-local.service.d
bluetooth.target.wants                  getty.target.wants           reboot.target.wants
dbus-fi.w1.wpa_supplicant1.service      [email protected]         remote-fs.target.wants
dbus-org.bluez.service                  graphical.target.wants       sockets.target.wants
dbus-org.freedesktop.Avahi.service      halt.target.wants            sshd.service
dbus-org.freedesktop.timesync1.service  multi-user.target.wants      sysinit.target.wants
default.target                          network-online.target.wants  syslog.service
dhcpcd5.service                         poweroff.target.wants        timers.target.wants
root@raspberrypi:/etc/systemd/system# cat dhcpcd5.service
[Unit]
Description=dhcpcd on all interfaces
Wants=network.target
Before=network.target

[Service]
Type=forking
PIDFile=/run/dhcpcd.pid
ExecStart=/usr/lib/dhcpcd5/dhcpcd -q -b
ExecStop=/sbin/dhcpcd -x

[Install]
WantedBy=multi-user.target
Alias=dhcpcd5.service

I think dhcpcd5 is dhcpcd service, do not know where it change name. How to fix it make dhcpcd service running correctly.

Answer 1

The reason it "fails" is because you caused dhcpcd to disable itself by including dhcp in /etc/network/interfaces.

You can only have ONE DHCP client

The error is listed in your Question:-

Oct 08 01:12:18 raspberrypi dhcpcd[284]: Not running dhcpcd because /etc/network/interfaces
Oct 08 01:12:18 raspberrypi dhcpcd[284]: defines some interfaces that will use a
Oct 08 01:12:18 raspberrypi dhcpcd[284]: DHCP client or static address

If you delete /etc/network/interfaces (which presumably you added for some reason) it would work; indeed it should work on a fresh installation if you don't modify anything.

See How to set up networking/WiFi