Debian 7 apt is upgrading my custom backported package with the "official" identical version!

Question

and happy new year to you all..

Recently I've built nginx deb package v1.4.4 from debian backport source that of course I've added to the apt sources.list and things went great.

I have run apt-get update then apt-get -V upgrade today to check how debian 7 apt would behave.. and this is what I got:

root@debian-lab:~/nginx-1.4.4-packages# apt-get -V upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
   nginx-full (1.4.4-1~bpo70+1 => 1.4.4-1~bpo70+1)
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/464 kB of archives.
After this operation, 9,027 kB disk space will be freed.
Do you want to continue [Y/n]?

As you can see, apt is trying to upgrade from (1.4.4-1~bpo70+1 => 1.4.4-1~bpo70+1), which is basically two identical version but my installed deb package has custom nginx modules added to default nginx-full and after the update, my custom modules are all gone and replaced by the standard debian wheezy backport deb.. I've built my nginx backport deb package from debian backport source and installed build-deb through the backport as well but some dependencies installed automatically from the stable that's what I saw from the verbose output..

Can you please help me to prevent this with an example? I heard about pinning, but is it the answer to my problem?

---

UPDATE

I've tried to apt pin the package and didn't work and here is the output i got:

apt-cache policy nginx-full
nginx-full:
Installed: 1.4.4-1~bpo70+1
Candidate: 1.4.4-1~bpo70+1
Version table:
 1.4.4-1~bpo70+1 0
    100 http://ftp.uk.debian.org/debian/ wheezy-backports/main amd64 Packages
*** 1.4.4-1~bpo70+1 0
    100 /var/lib/dpkg/status
 1.2.1-2.2+wheezy2 0
    500 http://ftp.uk.debian.org/debian/ wheezy/main amd64 Packages
    500 http://security.debian.org/ wheezy/updates/main amd64 Packages

And the following is the apt-cache policy nginx:

/etc/apt/preferences.d# apt-cache policy nginx
nginx:
  Installed: 1.4.4-1~bpo70+1
  Candidate: 1.4.4-1~bpo70+1
  Package pin: 1.4.4-1~bpo70+1
  Version table:
 *** 1.4.4-1~bpo70+1 1001
        100 http://ftp.uk.debian.org/debian/ wheezy-backports/main amd64 Packages
        100 /var/lib/dpkg/status
     1.2.1-2.2+wheezy2 1001
        500 http://ftp.uk.debian.org/debian/ wheezy/main amd64 Packages
        500 http://security.debian.org/ wheezy/updates/main amd64 Packages

But still apt is trying to upgrade and replace it!!

Sources.list content:

deb http://ftp.uk.debian.org/debian/ wheezy main
deb-src http://ftp.uk.debian.org/debian/ wheezy main

deb http://security.debian.org/ wheezy/updates main
deb-src http://security.debian.org/ wheezy/updates main

# wheezy-updates, previously known as 'volatile'
deb http://ftp.uk.debian.org/debian/ wheezy-updates main
deb-src http://ftp.uk.debian.org/debian/ wheezy-updates main

# Wheezy Backports repository
deb http://ftp.uk.debian.org/debian wheezy-backports main
deb-src http://ftp.uk.debian.org/debian wheezy-backports main

I've tried to apt pin once the package name 'nginx' and another time with nginx-full..

But both fail to hold the package!!!

Answer 1

To avoid problems, first, I would suggest you to use a custom (and greater) version number for your custom package, for example : 1.4.4-1~bpo70+1-mrsms. This would only be fair because your package is not the same exact version as the "official" backport. You can change the version number from the file debian/changelog before you build it.

You can test version comparison with dpkg (here, gt stands for "greater than", the return code is 0 if the expression is true):

$ dpkg --compare-versions 1.4.4-1~bpo70+1-mrsms gt 1.4.4-1~bpo70+1
$ echo $?

Be careful because your custom package will still be upgraded if an even greater version is found on the online repository. I would then suggest you to use pinning to avoid that (see man apt_preferences).

You may try this by creating a file, say /etc/apt/preferences.d/nginx-full, with this content:

Package: nginx-full
Pin: version 1.4.4-1~bpo70+1-mrsms
Pin-Priority: 1001

You can also hold the package in it's current installed state, that's very effectual, but not very elegant (might trouble future upgrades):

# aptitude hold nginx-full
# echo "nginx-full" hold |dpkg --set-selections

Answer 2

In chat, OP stated that he installed his package with dpkg --install. Additionally, IIRC, APT parses which package it prefers in the following way:

1. If a package is pinned, don't do anything with it.
2. Prefer whichever package known to the system has the highest program version.
3. If there are conflicts, prefer whichever package known to the system has the highest package version.
4. If there are still conflicts, prefer packages from a repository listed in /etc/apt/sources.list.
5. If there are still conflicts, prefer a package from whichever repository comes first in sources.list.

Armed with this information, we can posit that APT is choosing the repository version over the locally installed version at step 4. So, there are four ways to solve this problem:

1. Increase the package version to something beyond what the official Debian repositories provide. This will cause your locally installed package to be selected over the Debian package during step 3. (@Totor beat me to it, so I'll defer to his answer for instructions on how to do this.)
2. Increase the program version to something beyond what the official Debian repositories provide. This will get your package selected during step 2, but I would highly recommend not doing this and instead incrementing the package version - there's no technical reason, it's just more correct. However, if you do choose to do it this way, it is done in basically the same way as the package version, except that you change a different field in your debian/control file (or whatever else you are using to generate your package).
3. Pin your package. This will cause your package to be selected during step 1. Again, this is covered in @Totor's answer.
4. Create a local repository, put your package in it, and ensure that when you add it to your sources.list, it comes before the official Debian repositories. This will trigger a selection in step 5. In order to do this, refer to this Debian Wiki page. You may also be interested in this Ask Ubuntu question, if you want an easier tutorial-style reference.