I was looking through /usr/lib/x86_64-linux-gnu and noticed that some applications, such as gedit, ship with shared object files. I understand why libraries ship with shared libs, but what advantage is there for a stand-alone application to do the same?
Looking at the gedit example, it comes with following shared libraries:
/usr/lib64/gedit/libgedit.so
/usr/lib64/gedit/plugins/libdocinfo.so
/usr/lib64/gedit/plugins/libfilebrowser.so
/usr/lib64/gedit/plugins/libmodelines.so
/usr/lib64/gedit/plugins/libsort.so
/usr/lib64/gedit/plugins/libspell.so
/usr/lib64/gedit/plugins/libtime.so
The first one, libgedit.so, is for other applications that can reuse the editor component of gedit.
The rest of them are plugins for gedit. While they are built and distributed together with the application, they are independent addons and gedit should work without them too. 3rd party plugins could be there as well.
If someone want to write plugins for these application they can use a provided API which is usable by the shared libraries.
Also when you have multiple executables using the library in one software-package you can reduce the size of those binaries by shipping also a shared library instead of linking it staticly into each binary.
Related
Usually one rpm depends on many other packages or libs. This is not easy for massive deployment without internet access.
Since yum can automatically resolve dependencies. Is it possible to build a portable executable? So that we can copy it to other machines with the same OS.
If you want a known collection of RPMs to install, yum offers a downloadonly plugin. With that, you should be able to collect all the associated RPMs in one shot to install what you wanted on a disconnected machine.
The general way to build a binary without runtime library dependencies is to build it to be static, ie. using the -static argument to gcc, which links in static versions of the libraries required such that they're included in the resulting executable. This doesn't bundle in any data file dependencies or external executables (ie. libexec-style helpers), but simpler applications often don't need them.
For more complex needs (where data files are involved, or elements of the dependency chain can't be linked in for one reason or another), consider using AppImageKit -- which bundles an application and its dependency chain into a runnable ISO. See docs/links at PortableLinuxApps.org.
In neither of these cases does rpm or yum have anything to do with it. It's certainly possible to build an RPM that packages static executables, but that's a matter of changing the %build section of the spec file such that it passes -static to gcc, not of doing anything RPM-specific.
To be clear, by the way -- there are compelling reasons why we don't use static libraries all the time!
Using shared libraries means that applying a security update to a library only means replacing the library itself, not recompiling all applications using it.
Using shared libraries is more memory-efficient, since the single shared copy of the library in memory can be used by multiple applications.
Using shared libraries means your executables don't need to include full copies of all the libraries they use, making them much smaller.
I am working on bindings for a cpp library.
To do this I wrote a capi / wrapper for the library and compiled that to a shared lib (.so file).
My question is, how do I then use and integrate this file into cargo without forcing the user to install it? Currently I build the cpp via a Makefile called from the build variable in Cargo.toml, but I am unsure what to do with the compiled lib.
For testing, I can either use rpath or LD_LIBRARY_PATH to point the executable to the right location, but this will not work when distributing a library.
How are people managing this?
First of all, determine whether you really need a shared library. It's not clear from your question, but if you compiled your own wrapper into a shared library, that's probably unnecessary - you can compile your code into a static library and link it directly into your executable.
Moreover, you can try to link that third-party library statically too. I don't think this should be hard. And yes, you need to use build command in the manifest to do all of this now.
However, if you still need to use a shared library and you don't want the end user to install it herself (which is strange, because that's the point of shared libraries), you have to distribute it manually. For example, you can write a makefile which assembles an archive which your users may extract and use. For your program to find the library correctly you will either have the user to install this archive into the system root directory (e.g. /usr on linux; then this shared library will be located automatically) or you will have to write small shell script wrapper around your executable which will locate the shared library and set appropriate LD_LIBRARY_PATH.
I'd go for the first path. Usually all major platforms provide means to create installation packages (deb/rpm/pkg.tar.xz/whatever on Linux, brew on Mac, windows installer on Windows, though on Windows you can just put your shared library in the same directory as the executable and it will work). You just have to create packages for the platform your users work on, so your program will be installed in correct directories and your shared library will be resolved automatically.
Is it possible to stick a shared library to an app? I don't want to cross compile or anything like that. the shared library uses typical libraries which are available on target systems( i.e. Ubuntu 32bit x86) according to 'ldd'.
If there is a staticly built version of the library available (libxxx.a instead of libxxx.so), the easiest way would be to link against that. If that is not possible, you could create something like a self-extracting executable tar file with the app and the shared library. For example, see http://www.linuxjournal.com/content/add-binary-payload-your-shell-scripts
I have read that .so is a dynamic library file and .a is a static library file.
While building openssl i gave the option ./Configure no-shared and it created a lot of .a files.
So, my question is will the other packages like apache will be able to use .a files from openssl?
for example libcrypto.a,
someone please advice me if im going enirely through wrong path.
Basically the static library can be compiled into another application at link time. In your example Apache could use libcrypto.a during build time and include it in the Apache httpd application.
A dynamic .so library can be loaded and unloaded at runtime and you have a better flexibility to change what Apache should support without recompiling the Apache binaries.
Using Apache as example the dynamic loading of .so files are described in the Dynamic Shared Object (DSO) section in the documentation. You can also find links to the installation section which describe how to include static libraries at build time.
There is a good question about this that could be good to read, and that provide mote details in the subject.
Difference between shared objects (.so), static libraries (.a), and DLL's (.so)?
If A.a is static library and two different programs want to use it. A.a is created two times for each program. while If A.so is dynamic library than two programs access same file.
Its mean that you are using reference in library.
If your library is going to be shared among several executables(like apache and openssl), it often makes sense to make it dynamic to reduce the size of the executables. Otherwise, definitely make it static.
In your case you must create dynamic library
Please read -
http://www.yolinux.com/TUTORIALS/LibraryArchives-StaticAndDynamic.html.
It is a very good tutorial with example.
you will learn -
what is static library (.a) and how to make it.
what is shared library (.so) and how to make it.
difference with .ddl (windows os)
I am developing cross-platform Qt application.
It is freeware though not open-source. Therefore I want to distribute it as a compiled binary.
On windows there is no problem, I pack my compiled exe along with MinGW's and Qt's DLLs and everything goes great.
But on Linux there is a problem because the user may have shared libraries in his/her system very different from mine.
Qt deployment guide suggests two methods: static linking and using shared libraries.
The first produces huge executable and also require static versions of many libraries which Qt depends on, i.e. I'll have to rebuild all of them from scratches. The second method is based on reconfiguring dynamic linker right before the application startup and seems a bit tricky to me.
Can anyone share his/her experience in distributing Qt applications under Linux? What method should I use? What problems may I confront with? Are there any other methods to get this job done?
Shared libraries is the way to go, but you can avoid using LD_LIBRARY_PATH (which involves running the application using a launcher shell script, etc) building your binary with the -rpath compiler flag, pointing to there you store your libraries.
For example, I store my libraries either next to my binary or in a directory called "mylib" next to my binary. To use this on my QMake file, I add this line in the .pro file:
QMAKE_LFLAGS += -Wl,-rpath,\\$\$ORIGIN/lib/:\\$\$ORIGIN/../mylib/
And I can run my binaries with my local libraries overriding any system library, and with no need for a launcher script.
You can also distribute Qt shared libraries on Linux. Then, get your software to load those instead of the system default ones. Shared libraries can be over-ridden using the LD_LIBRARY_PATH environment variable. This is probably the simplest solution for you. You can always change this in a wrapper script for your executable.
Alternatively, just specify the minimum library version that your users need to have installed on the system.
When we distribute Qt apps on Linux (or really any apps that use shared libraries) we ship a directory tree which contains the actual executable and associated wrapper script at the top with sub-directories containing the shared libraries and any other necessary resources that you don't want to link in.
The advantage of doing this is that you can have the wrapper script setup everything you need for running the application without having to worry about having the user set environment variables, install to a specific location, etc. If done correctly, this also allows you to not have to worry about from where you are calling the application because it can always find the resources.
We actually take this tree structure even further by placing all the executable and shared libraries in platform/architecture sub-directories so that the wrapper script can determine the local architecture and call the appropriate executable for that platform and set the environment variables to find the appropriate shared libraries. We found this setup to be particularly helpful when distributing for multiple different linux versions that share a common file system.
All this being said, we do still prefer to build statically when possible, Qt apps are no exception. You can definitely build with Qt statically and you shouldn't have to go build a lot of additional dependencies as krbyrd noted in his response.
sybreon's answer is exactly what I have done. You can either always add your libraries to LD_LIBRARY_PATH or you can do something a bit more fancy:
Setup your shipped Qt libraries one per directory. Write a shell script, have it run ldd on the executable and grep for 'not found', for each of those libraries, add the appropriate directory to a list (let's call it $LDD). After you have them all, run the binary with LD_LIBRARY_PATH set to it's previous value plus $LDD.
Finally a comment about "I'll have to rebuild all of them from scratches". No, you won't have to. If you have the dev packages for those libraries, you should have .a files, you can statically link against these.
Not an answer as such (sybreon covered that), but please note that you are not allowed to distribute your binary if it is statically linked against Qt, unless you have bought a commercial license, otherwise your entire binary falls under the GPL (or you're in violation of Qt's license.)
If you have a commercial license, never mind.
If you don't have a commercial license, you have two options:
Link dynamically against Qt v4.5.0 or newer (the LGPL versions - you may not use the previous versions except in open source apps), or
Open your source code.
The probably easiest way to create a Qt application package on Linux is probably linuxdeployqt. It collects all required files and lets you build an AppImage which runs on most Linux distributions.
Make sure you build the application on the oldest still-supported Ubuntu LTS release so your AppImage can be listed on AppImageHub.
You can look into QtCreator folder and use it as an example. It has qt.conf and qtcreator.sh files in QtCreator/bin.
lib/qtcreator is the folder with all needed Qt *.so libraries. Relative path is set inside qtcreator.sh, which should be renamed to you-app-name.sh
imports,plugins,qml are inside bin directory. Path to them is set in qt.conf file. This is needed for QML applications deployment.
This article has information on the topic. I will try it myself:
http://labs.trolltech.com/blogs/2009/06/02/deploying-a-browser-on-gnulinux/
In a few words:
Configure Qt with -platform linux-lsb-g++
Linking should be done
with –lsb-use-default-linker
Package everything and deploy (will
need a few tweaks here but I haven't yet tried it sorry)