dhcpcd and dhcpcd-run-hooks on Raspbian

Written by pmd - - no comments

If you are using Raspbian GNU/Linux 9 (stretch), then you are most likely using dhcpcd as your DHCP and DHCPv6 client. How to know your OS version? Here :

$ cat /etc/os-release
PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
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"
  • dhcpcd gets the host information (IP address, routes, etc) from a DHCP server and configures the network interface of the machine on which it is running. Manual of DHCPCD(8).
  • dhcpcd-run-hooks is a DHCP client configuration script. It is used by dhcpcd to run any system and user defined hook scripts. Manual of DHCPCD-RUN-HOOKS(8).

dhcpcd

It seems that to restart all network interfaces this works :

$ sudo systemctl restart dhcpcd.service

To understand what happened, better read dhcpcd logs, here is what we can see:

$ journalctl -u dhcpcd
Dec 21 15:38:04 raspberrypi systemd[1]: Stopping dhcpcd on all interfaces...
Dec 21 15:38:04 raspberrypi dhcpcd[15174]: sending signal TERM to pid 14888
Dec 21 15:38:04 raspberrypi dhcpcd[15174]: waiting for pid 14888 to exit
Dec 21 15:38:04 raspberrypi dhcpcd[14888]: received SIGTERM, stopping
Dec 21 15:38:04 raspberrypi dhcpcd[14888]: eth0: removing interface
Dec 21 15:38:04 raspberrypi dhcpcd[14888]: wlan0: removing interface
Dec 21 15:38:04 raspberrypi dhcpcd[15174]: sending signal TERM to pid 14888
Dec 21 15:38:04 raspberrypi dhcpcd[15174]: waiting for pid 14888 to exit
Dec 21 15:38:05 raspberrypi systemd[1]: Stopped dhcpcd on all interfaces.
Dec 21 15:38:05 raspberrypi systemd[1]: Starting dhcpcd on all interfaces...
Dec 21 15:38:05 raspberrypi dhcpcd[15180]: dev: loaded udev
Dec 21 15:38:05 raspberrypi systemd[1]: Started dhcpcd on all interfaces.
Dec 21 15:38:05 raspberrypi dhcpcd-run-hooks[15203]: wlan0: starting wpa_supplicant
Dec 21 15:38:05 raspberrypi dhcpcd[15185]: eth0: waiting for carrier
Dec 21 15:38:05 raspberrypi dhcpcd[15185]: wlan0: waiting for carrier
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: carrier acquired
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: DUID 00:01:00:01:21:b0:de:63:b8:27:eb:4d:6c:87
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: IAID eb:5d:6d:97
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: adding address fe80::2882:e851:cf0c:9242
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: soliciting an IPv6 router
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: rebinding lease of 192.168.254.200
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: leased 192.168.254.200 for 86400 seconds
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: adding route to 192.168.254.0/24
Dec 21 15:38:06 raspberrypi dhcpcd[15185]: wlan0: adding default route via 192.168.254.1
Dec 21 15:38:19 raspberrypi dhcpcd[15185]: wlan0: no IPv6 Routers available

Source

dhcpcd-run-hooks

dhcpcd runs /lib/dhcpcd/dhcpcd-run-hooks. This script runs each script found in /lib/dhcpcd/dhcpcd-hooks in a lexical order.
dhcpcd-run-hooks is used by dhcpcd to run any system and user defined hook scripts. System hook scripts are found in /lib/dhcpcd/dhcpcd-hooks.
There is a list of reasons why dhcpcd-run-hooks could be invoked, such as BOUND (= dhcpcd obtained a new lease from a DHCP server = computer has an IP assigned on the interface).
Many variables will then be set, along with any protocol supplied ones, such as :

  • $interface : the name of the interface
  • $reason : reason why dhcpcd-run-hooks was invoked
  • $if_up : true if the interface is up, otherwise false.

To know what is the current IPv4 address after an interface BOUNDed dhcpcd obtained a new lease from a DHCP server.:

ifconfig $interface | grep "inet " | awk '{print $2}'

I created /lib/dhcpcd/dhcpcd-hooks/60-test_by_pmd in order to play with this functionality. Shell script I used in order to check IP after new DHCP lease was obtained (writing output in /home/pi/test.txt in order to see what happened afterward):

if [ "$reason" = "BOUND" ] && [ "$if_up" = "true" ]; then
     echo "$(date +"%d-%m-%y %H:%M:%S ") $reason $interface IP:$if_up DOWN:$if_down" >> /home/pi/test.txt
     ifconfig $interface | grep "inet " | awk '{print $2}' >> /home/pi/test.txt
fi

Sources : both manuals.

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