Skip to main content

debian - Managing maintainer scripts for packages with multple .debs

If you've ever installed a package from command line on Linux, you must have noticed two main prompts related to package configuration: one asking what to do with installed configuration files with local changes, and one providing feedback right after the installation/upgrade/removal/purge has completed.

Under Debian the latter was most probably the postinst script, one of the Package Maintainer Scripts which is executed after installation and configuration.

These diagrams are very useful to understand what happens to the Maintainer Scripts in different circumstances: first installation, upgrade, removal, purge.

Their name is probably self-explanatory: preinst, postinst, prerm, postrm. Each of them takes zero or more arguments depending on the scenario. It can help to understand that those are really just scripts executed by dpkg - and typically they are shell scripts, sometimes with interactive prompts.

If you're building your own packages, you surely already have one of more of those scripts in the source debian/ directory. They are automatically included in the .deb by dpkg-buildpackage (or any of its wrappers) during the build.

What you may find interesting - and this is the purpose of this article - is that if you're building multiple .deb packages from the same debian/ directory (i.e. using the same debian/control makefile), having for example a single postinst script is not sufficient. Only the first built .deb will contain it, while the others won't.
The symptom in this example is that when installing the packages other than the first built, you won't see any of the prompts, feedback or actions you are delegating to postinst.

To fix this, it's sufficient to include for example a postinst script per package:
debian/control
debian/rules
[...]
debian/package_1.postinst
debian/package_2.postinst
debian/package_3.postinst

In case you're wondering, yes, you can have a single postinst script and just create a symbolic link to it for each package.

Labels:

Popular posts from this blog

Troubleshooting TURN

  WebRTC applications use the ICE negotiation to discovery the best way to communicate with a remote party. I t dynamically finds a pair of candidates (IP address, port and transport, also known as “transport address”) suitable for exchanging media and data. The most important aspect of this is “dynamically”: a local and a remote transport address are found based on the network conditions at the time of establishing a session. For example, a WebRTC client that normally uses a server reflexive transport address to communicate with an SFU. when running inside the home office, may use a relay transport address over TCP when running inside an office network which limits remote UDP targets. The same configuration (defined as “iceServers” when creating an RTCPeerConnection will work in both cases, producing different outcomes.
Read more

Extracting RTP streams from network captures

I needed an efficient way to programmatically extract RTP streams from a network capture. In addition I wanted to: save each stream into a separate pcap file. extract SRTP-negotiated keys if present and available in the trace, associating them to the related RTP (or SRTP if the negotiation succeeded) stream. Some caveats: In normal conditions the negotiation of SRTP sessions happens via a secure transport, typically SIP over TLS, so the exchanged crypto information may not be available from a simple network capture. There are ways to extract RTP streams using Wireshark or tcpdump; it’s not necessary to do it programmatically. All this said I wrote a small tool ( https://github.com/giavac/pcap_tool ) that parses a network capture and tries to interpret each packet as either RTP/SRTP or SIP, and does two main things: save each detected RTP/SRTP stream into a dedicated pcap file, which name contains the related SSRC. print a summary of the crypto information exchanged, if available. With ...
Read more

Testing SIP platforms and pjsip

There are various levels of testing, from unit to component, from integration to end-to-end, not to mention performance testing and fuzzing. When developing or maintaining Real Time Communications (RTC or VoIP) systems,  all these levels (with the exclusion maybe of unit testing) are made easier by applications explicitly designed for this, like sipp . sipp has a deep focus on performance testing, or using a simpler term, load testing. Some of its features allow to fine tune properties like call rate, call duration, simulate packet loss, ramp up traffic, etc. In practical terms though once you have the flexibility to generate SIP signalling to negotiate sessions and RTP streams, you can use sipp for functional testing too. sipp can act as an entity generating a call, or receiving a call, which makes it suitable to surround the system under test and simulate its interactions with the real world. What sipp does can be generalised: we want to be able to simulate the real world tha...
Read more