It happens sometimes that an error is discovered in an installed package, and it should be fixed sooner - rather than later. This recipe describes one way to do that. The example is an error I discovered in dhcpcd, the default network management package for Raspberry Pi OS.
I discovered the error used as the example here using the inform option in dhcpcd.conf. Using inform set up an "infinite loop" in the code, and created a tsunami of log activity - not good for SD card life. It wasn't a debilitating error, but neither is it one that could wait for 6 months - or even 3 years as this seems to be the last time the repo was modified.
Just for background, the inform option is set in /etc/dhcpcd.conf to create a stable/fixed IPv4 address for your system. If your network manager is dhcpcd, you may have encountered the inform option. If you've created a fixed ip address in dhcpcd.conf, but have not used the inform option, then you have done it incorrectly - or at least inefficiently. But why to use the inform option is another subject; this is about patching dhcpcd to correct an error when the inform option has been set in dhcpcd.conf.
Since I have zero experience with building and changing source files managed under Debian-based systems, I'll have to write this recipe on that basis! If you have no experience, this is the guide for you :)
First step is to make certain the deb-src repos are available to apt for fetching source files
$ cat /etc/apt/sources.list
deb http://raspbian.raspberrypi.org/raspbian/ bullseye main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
deb-src http://raspbian.raspberrypi.org/raspbian/ bullseye main contrib non-free rpi
$ $ cat /etc/apt/sources.list.d/raspi.list
deb http://archive.raspberrypi.org/debian/ bullseye main
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
deb-src http://archive.raspberrypi.org/debian/ bullseye main
$ sudo apt update # update sources.list, raspi.list & any others addedUnless you just know the name of the package, it will be necessary to search for it; e.g. we're looking for dhcpcd, so try this:
$ apt-cache search dhcpcd
dhcpcd - DHCP client for automatically configuring IPv4 networking
dhcpcd-dbus - DBus bindings for dhcpcd
dhcpcd-gtk - GTK+ frontend for dhcpcd and wpa_supplicant
dhcpcd5 - DHCPv4, IPv6RA and DHCPv6 client with IPv4LL support
dhcpcd5-dbgsym - debug symbols for dhcpcd5
lxplug-network - Network plugin for lxpanelIn this case, a little research indicates that dhcpcd5 is the package of interest.
To find the source packages, we use the showsrc option to display all versions of the source package records.
$ apt-cache showsrc dhcpcd5
# interesting/relevant lines follow:
Package: dhcpcd5
Binary: dhcpcd5
Version: 1:8.1.2-1+rpt5
Homepage: https://roy.marples.name/projects/dhcpcd
Vcs-Browser: https://salsa.debian.org/smlx-guest/dhcpcd5
Vcs-Git: https://salsa.debian.org/smlx-guest/dhcpcd5.git
#
# NOTE two packages are listed for dhcpcd5
# 'Version: 1:8.1.2-1+rpt5' appears to be the correct one as dhcpcd --version ==> 8.1.2
...
$ Searching and reading through various sources, the following sequence was pieced together:
$ sudo apt install devscripts # build tools for using `debuild`
$ apt-get source dhcpcd5
# ... several compressed files, and a directory named ~/dhcpcd5-8.1.2 were downloaded
$ cd dhcpcd5-8.1.2 # cd to source dir
~/dhcpcd5-8.1.2 $ nano src/dhcp.c # make required changes to the source
# you can download the dhcp.c file with the 1-line change from the `source` folder
# here on GitHub; just copy over the same filename in ~/dhcpcd5-8.1.2/src
~/dhcpcd5-8.1.2 $ debuild -b -uc -us
## you may get an 'unmet dependencies' error; I did when building on 'buster':
## dpkg-checkbuilddeps: error: Unmet build dependencies: libudev-dev
## if so, this should fix it (REF: https://unix.stackexchange.com/a/416517/286615)
$ mk-build-deps --install --root sudo --remove
## and then run debuild again =>
~/dhcpcd5-8.1.2 $ debuild -b -uc -us
$ cd ..
$ sudo dpkg -i dhcpcd5_8.1.2-1+rpt5_armhf.deb # or whatever the name of the .deb file
$ dhcpcd --version
dhcpcd 8.1.2
$ If you got to this point, you have successfully built and installed the dhcpcd5 package!
If you patched (or copied the revised) dhcp.c file into ~/dhcpcd5-8.1.2/src before you built and installed the .deb file, you now have an updated dhcpcd!! (even tho' the version # reported by dhcpcd --version remains the same)
You may also want to put a "hold" on the package to prevent it from being over-written with the un-patched version during an 'apt upgrde'. The RPi Organization does not use the git repos advertised in 'apt-cache showsrc dhcpcd5', and my "merge request" had to be submitted manually. Consequently I really do not know when or if the RPi Organization will incorporate this patch. If not, we may need to patch this indefinitely. To put a hold on 'dhcpcd' using 'apt' (REF) is simple:
$ sudo apt-mark hold dhcpcd5
## to remove the hold:
$ sudo apt-mark unhold dhcpcd5The dpkg tool will come in handy; e.g.:
$ dpkg -l dhcpcd5
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-==============-============-====================================================
ii dhcpcd5 1:8.1.2-1+rpt5 armhf DHCPv4, IPv6RA and DHCPv6 client with IPv4LL support