How do I get apt-get to ignore some dependencies?

Question

How do I make apt-get ignore some dependencies? For example, I wanted to install mailx so I can use it to send email from cron scripts/report-generating tools. However, installing mailx also installs exim4 and a whole bunch of dependencies (I already have Postfix installed) I don't really need and which I guess mailx can also live without.

How do I ignore some dependencies but still use apt-get since it's a nice tool?

Answer 1

You can try the --nodeps flag with apt-get.
Or download the package and install it using dpkg with the option --ignore-depends.

Answer 2

Since you installed postfix from source, you need to install a "dummy" package which will satisfy the mail-transport-agent dependency of mailx (or bsd-mailx). The "equivs" package in debian exists to create such a dummy package which you can install to tell dpkg "this dependency is satisfied"

The reason that telling dpkg to simply ignore dependencies is not a good solution, is that you are only telling dpkg/apt to ignore it for a single transaction, you can't tell it to ignore dependencies forever. Everytime you use apt it checks the dependencies on all packages

Answer 3

On my debian system, bsd-mailx actually depends on default-mta | mail-transport-agent (you can check what a package depends on with apt-cache show <pkg> for anything in the archive or dpkg -s <pkg> for installed packages.

It may be that your postfix package doesn't have Provides: mail-transport-agent so apt doesn't realize you have an MTA installed. It would be worth filing a bug for that if it's an official package.

Answer 4

For the purposes of this, you could just install nail which I don't think has these dependencies?

apt-get install nail

Answer 5

The dependencies required when you install a package through apt are listed by the package builder. So whoever built the mailx package decided that exim4 was a requirement (maybe mailx uses one of exim4's libraries?)

An alternative is to build mailx from source, and download the necessary libraries to do this. This will avoid involving the package manager.

Answer 6

You can change the dependencies of a deb package like this:

1. Unpack deb: ar x golden-linux.deb (will create i.e. three files: debian-binary control.tar.gz data.tar.gz)
2. Unpack control archive: tar xzf control.tar.gz (will create: postinst postrm preinst prerm md5sums control)
3. Fix dependencies in control (use a text editor)
4. Repack control.tar.gz: tar c {post,pre}{inst,rm} md5sums control | gzip -c > control.tar.gz
5. Repack deb: ar rcs newpackage.deb debian-binary control.tar.gz data.tar.gz (order important! See [Note] )

[Note]: dpkg wouldn't be able to read the metadata of a package quickly if it had to search for where the data section ended!