How do Linux programs know where the library files are and how to call them? - linux

When I install a program using apt-get install, it tells me which dependency libraries also need to be installed.
For example, Nginx requires libgd3 (3d graphics library) to be installed.
When Nginx needs to call code in libgd3 how does it know where the file is and
How does it actually go about it? I assume it must load it into the Nginx process heap and then use some kind of function table to make calls?
I am not sure how this process works, thanks.

The libraries are in standard path usually /usr/lib which the linker searches during linking. The dynamic libraries are called shared objects in linux having the extension .so .
Check this link to know more about Linux Libraries:
http://www.yolinux.com/TUTORIALS/LibraryArchives-StaticAndDynamic.html

Usually through the environment variable LD_LIBRARY_PATH which is set of directories where libraries should be searched for first
See what it is set to :
env | grep LD_LIBRARY_PATH
You can update the new location to search temporarily by
export $LD_LIBRARY_PATH = $LD_LIBRARY_PATH:/new/dir/to/look
There is every chance that this env variable is not present in your distro. So you can try the below
1) Add library directories to /etc/ld.so.conf or
2) add it to the library cache by using ldconfig
Please read more here
http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

Related

Portable .so installation script on linux

Is there an accepted way to install shared object libraries on linux? I am writing a script which needs to install to /usr/local/lib64/ on some distributions (like RHEL) and to /usr/local/lib/ on others (like Ubuntu).
Is there a way to detect the location that so files should be installed to?
Some possibilities that I have considered:
Read the contents of /etc/ld.so.conf.d/* to check for paths searched by the dynamic linker.
Run ldconfig -p to see where most libraries are installed and make some programatic decision based on that
Check the distribution and use a decoder in the script

Can I avoid exporting LD_LIBRARY_PATH by hardcoding library paths in the executable?

I'm zipping a pre-built (no source/object files) binary application for distribution. The binary application requires a couple of libraries not included by default. The only way I seem to be able to get the application to start on the end-user is by including a run.sh that sets the library path to the current directory:
export LD_LIBRARY_PATH=./:$LD_LIBRARY_PATH
./MyApp.out
However, I'd really like to allow the user to just unzip the zip and doubleclick MyApp.out (without the shell script). Can I edit MyApp.out to search the current directory for the library? I've done something similar on OSX using install_name_tool, but that tool isn't available here.
You want to set the rpath. See this answer. So link using
gcc yourobjects*.o -L/some/lib/dir/ -lsome -Wl,-rpath,.
But you might want even to use -Wl,-rpath,$PWD or perhaps -Wl,-rpath,'$ORIGIN'. See this.
You could also (and this should work for a pre-built executable) configure your /etc/ld.so.conf by adding a line there with an absolute path (of the directory containing the lib), then running ldconfig -v ... See ldconfig(8)
I would suggest adding /usr/local/lib into /etc/ld.so.conf and making a symlink from /usr/local/lib/libfoo.so to e.g. $HOME/libfoo.so etc... (then run ldconfig ...). I don't think adding a user specific directory to /etc/ld.so.conf is reasonable ...
PS. What you really want is to package your application (e.g. as a *.deb package for Debian or Ubuntu, or an *.rpm for Fedora or Redhat). Package management systems handle dependencies!

Looking for missing shared library

On a Linux system, I am trying to run a Fortran program that makes use of some shared libraries (netCDF libs, if that makes a difference). Before I run, I set LD_LIBRARY_PATH so that it points to the location of my libraries. Then I run the executable and I quickly get the error
../my_program: error while loading shared libraries: libnetcdff.so.5: cannot open shared object file: No such file or directory
Now, I double check the value of LD_LIBRARY_PATH, and then cd to it and find plain as day
$ ls *ff*
$ libnetcdff.a libnetcdff.la libnetcdff.so libnetcdff.so.0 libnetcdff.so.0.0.0
So the libnetcdff is absolutely present.
Could anyone point me to the problem?
The one thing that has occurred to me is that the executable seems to want to find libnetcdff.so.5, while the library that is present is actually libnetcdff.so.0. Is that the problem? If so, is there a way to convince the executable to not insist on "5"? Alternatively, would a link from libnetcdff.so.0 to libnetcdff.so.5 solve the problem? (I don't have permissions in the directory, BTW, which is why I haven't tried that yet.)
Environment info: CentOS machine, code compiled with gfortran. And yes, when I compiled, my -L flags were pointing to the same directory that LD_LIBRARY_PATH points to.
Thanks.
A library link should work. Since you mention that you do not have root/sudo access, what you can do is link in a file you do have access in:
ln -s /path/to/libnetcdff.so.0 /path/you/have/access/to/libnetcdff.so.5
And then add in the /path/you/have/access/to/ in your LD_LIBRARY_PATH.

How to link shared libraries in local directory, OSX vs Linux

I have some shared/dynamic libraries installed in a sandbox directory. I'm building some applications which link agains the libraries. I'm running into what appears to be a difference between OSX and Linux in this regard and I'm not sure what the (best) solution is.
On OSX the location of library itself is recorded into the library, so that if your applications links against it, the executable knows where to look for the library at runtime. This works like expected with my sandbox, because the executable looks there instead of system wide install paths.
On Linux I can't get this to work. Apparently the library location is not present in the library itself. As I understand it you have to add the folders which contain libraries to /etc/ld.so.conf and regenerate the ld cache by running ldconfig.
This doesn't seem to do the trick for me because my libraries are located inside a users home directory. It looks like ldconfig doesn't like that, which makes sense actually.
How can I solve this? I don't want to move the libraries out of my sandbox.
On Linux, run your program with the environment variable LD_LIBRARY_PATH set to your sandbox dir.
(I remember having used a flag -R to include library paths in the binary, but either it has been removed from gcc or it was only available on BSD systems.)
On Linux you should set LD_RUN_PATH to your sandbox dir. This is better than setting LD_LIBRARY_PATH because you're telling the linker where the library is at link time, rather than telling the shared library loader at run time.
See: Link

Linux error while loading shared libraries: cannot open shared object file: No such file or directory

Program is part of the Xenomai test suite, cross-compiled from Linux PC into Linux+Xenomai ARM toolchain.
# echo $LD_LIBRARY_PATH
/lib
# ls /lib
ld-2.3.3.so libdl-2.3.3.so libpthread-0.10.so
ld-linux.so.2 libdl.so.2 libpthread.so.0
libc-2.3.3.so libgcc_s.so libpthread_rt.so
libc.so.6 libgcc_s.so.1 libstdc++.so.6
libcrypt-2.3.3.so libm-2.3.3.so libstdc++.so.6.0.9
libcrypt.so.1 libm.so.6
# ./clocktest
./clocktest: error while loading shared libraries: libpthread_rt.so.1: cannot open shared object file: No such file or directory
Is the .1 at the end part of the filename? What does that mean anyway?
Your library is a dynamic library.
You need to tell the operating system where it can locate it at runtime.
To do so,
we will need to do those easy steps:
Find where the library is placed if you don't know it.
sudo find / -name the_name_of_the_file.so
Check for the existence of the dynamic library path environment variable(LD_LIBRARY_PATH)
echo $LD_LIBRARY_PATH
If there is nothing to be displayed, add a default path value (or not if you wish to)
LD_LIBRARY_PATH=/usr/local/lib
We add the desired path, export it and try the application.
Note that the path should be the directory where the path.so.something is. So if path.so.something is in /my_library/path.so.something, it should be:
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/my_library/
export LD_LIBRARY_PATH
./my_app
Reference to source
Here are a few solutions you can try:
ldconfig
As AbiusX pointed out: If you have just now installed the library, you may simply need to run ldconfig.
sudo ldconfig
ldconfig creates the necessary links and cache to the most recent
shared libraries found in the directories specified on the command
line, in the file /etc/ld.so.conf, and in the trusted directories
(/lib and /usr/lib).
Usually your package manager will take care of this when you install a new library, but not always, and it won't hurt to run ldconfig even if that is not your issue.
Dev package or wrong version
If that doesn't work, I would also check out Paul's suggestion and look for a "-dev" version of the library. Many libraries are split into dev and non-dev packages. You can use this command to look for it:
apt-cache search <libraryname>
This can also help if you simply have the wrong version of the library installed. Some libraries are published in different versions simultaneously, for example, Python.
Library location
If you are sure that the right package is installed, and ldconfig didn't find it, it may just be in a nonstandard directory. By default, ldconfig looks in /lib, /usr/lib, and directories listed in /etc/ld.so.conf and $LD_LIBRARY_PATH. If your library is somewhere else, you can either add the directory on its own line in /etc/ld.so.conf, append the library's path to $LD_LIBRARY_PATH, or move the library into /usr/lib. Then run ldconfig.
To find out where the library is, try this:
sudo find / -iname *libraryname*.so*
(Replace libraryname with the name of your library)
If you go the $LD_LIBRARY_PATH route, you'll want to put that into your ~/.bashrc file so it will run every time you log in:
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/to/library
Update
While what I write below is true as a general answer about shared libraries, I think the most frequent cause of these sorts of message is because you've installed a package, but not installed the -dev version of that package.
Well, it's not lying - there is no libpthread_rt.so.1 in that listing. You probably need to re-configure and re-build it so that it depends on the library you have, or install whatever provides libpthread_rt.so.1.
Generally, the numbers after the .so are version numbers, and you'll often find that they are symlinks to each other, so if you have version 1.1 of libfoo.so, you'll have a real file libfoo.so.1.0, and symlinks foo.so and foo.so.1 pointing to the libfoo.so.1.0. And if you install version 1.1 without removing the other one, you'll have a libfoo.so.1.1, and libfoo.so.1 and libfoo.so will now point to the new one, but any code that requires that exact version can use the libfoo.so.1.0 file. Code that just relies on the version 1 API, but doesn't care if it's 1.0 or 1.1 will specify libfoo.so.1. As orip pointed out in the comments, this is explained well at here.
In your case, you might get away with symlinking libpthread_rt.so.1 to libpthread_rt.so. No guarantees that it won't break your code and eat your TV dinners, though.
You need to ensure that you specify the library path during
linking when you compile your .c file:
gcc -I/usr/local/include xxx.c -o xxx -L/usr/local/lib -Wl,-R/usr/local/lib
The -Wl,-R part tells the resulting binary to also look for the library
in /usr/local/lib at runtime before trying to use the one in /usr/lib/.
Try adding LD_LIBRARY_PATH, which indicates search paths, to your ~/.bashrc file
LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path_to_your_library
It works!
The linux.org reference page explains the mechanics, but doesn't explain any of the motivation behind it :-(
For that, see Sun Linker and Libraries Guide
In addition, note that "external versioning" is largely obsolete on Linux, because symbol versioning (a GNU extension) allows you to have multiple incompatible versions of the same function to be present in a single library. This extension allowed glibc to have the same external version: libc.so.6 for the last 10 years.
cd /home/<user_name>/
sudo vi .bash_profile
add these lines at the end
LD_LIBRARY_PATH=/usr/local/lib:<any other paths you want>
export LD_LIBRARY_PATH
Another possible solution depending on your situation.
If you know that libpthread_rt.so.1 is the same as libpthread_rt.so then you can create a symlink by:
ln -s /lib/libpthread_rt.so /lib/libpthread_rt.so.1
Then ls -l /lib should now show the symlink and what it points to.
I had a similar error and it didn't fix with giving LD_LIBRARY_PATH in ~/.bashrc .
What solved my issue is by adding .conf file and loading it.
Go to terminal an be in su.
gedit /etc/ld.so.conf.d/myapp.conf
Add your library path in this file and save.(eg: /usr/local/lib).
You must run the following command to activate path:
ldconfig
Verify Your New Library Path:
ldconfig -v | less
If this shows your library files, then you are good to go.
running:
sudo ldconfig
was enough to fix my issue.
I had this error when running my application with Eclipse CDT on Linux x86.
To fix this:
In Eclipse:
Run as -> Run configurations -> Environment
Set the path
LD_LIBRARY_PATH=/my_lib_directory_path
Wanted to add, if your libraries are in a non standard path, run ldconfig followed by the path.
For instance I had to run:
sudo ldconfig /opt/intel/oneapi/mkl/2021.2.0/lib/intel64
to make R compile against Intel MKL
All I had to do was run:
sudo apt-get install libfontconfig1
I was in the folder located at /usr/lib/x86_64-linux-gnu and it worked perfectly.
Try to install lib32z1:
sudo apt-get install lib32z1
If you are running your application on Microsoft Windows, the path to dynamic libraries (.dll) need to be defined in the PATH environment variable.
If you are running your application on UNIX, the path to your dynamic libraries (.so) need to be defined in the LD_LIBRARY_PATH environment variable.
The error occurs as the system cannot refer to the library file mentioned. Take the following steps:
Running locate libpthread_rt.so.1 will list the path of all the files with that name. Let's suppose a path is /home/user/loc.
Copy the path and run cd home/USERNAME. Replace USERNAME with the name of the current active user with which you want to run the file.
Run vi .bash_profile and at the end of the LD_LIBRARY_PATH parameter, just before ., add the line /lib://home/usr/loc:.. Save the file.
Close terminal and restart the application. It should run.
I got this error and I think its the same reason of yours
error while loading shared libraries: libnw.so: cannot open shared
object file: No such file or directory
Try this. Fix permissions on files:
cd /opt/Popcorn (or wherever it is)
chmod -R 555 * (755 if not ok)
I use Ubuntu 18.04
Installing the corresponding -dev package worked for me,
sudo apt install libgconf2-dev
Before installing the above package, I was getting the below error:
turtl: error while loading shared libraries: libgconf-2.so.4: cannot open shared object file: No such file or directory
I got this error and I think its the same reason of yours
error while loading shared libraries: libnw.so: cannot open shared object
file: No such file or directory
Try this. Fix permissions on files:
sudo su
cd /opt/Popcorn (or wherever it is)
chmod -R 555 * (755 if not ok)
chown -R root:root *
A similar problem can be found here.
I've tried the mentioned solution and it actually works.
The solutions in the previous questions may work. But the following is an easy way to fix it.
It works by reinstalling the package libwbclient
in fedora:
dnf reinstall libwbclient
You can read about libraries here:
https://domiyanyue.medium.com/c-development-tutorial-4-static-and-dynamic-libraries-7b537656163e

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