CODEWITHSUNDEEP
pythonshared-librariesenvironment-variables
Anurag Uniyal
Anurag Uniyal

Reputation: 88777

Change current process environment's LD_LIBRARY_PATH

Is it possible to change environment variables of current process?

More specifically in a python script I want to change LD_LIBRARY_PATH so that on import of a module 'x' which depends on some xyz.so, xyz.so is taken from my given path in LD_LIBRARY_PATH

is there any other way to dynamically change path from where library is loaded?

Edit: I think I need to mention that I have already tried thing like os.environ["LD_LIBRARY_PATH"] = mypath os.putenv('LD_LIBRARY_PATH', mypath)

but these modify the env. for spawned sub-process, not the current process, and module loading doesn't consider the new LD_LIBRARY_PATH

Edit2, so question is can we change environment or something so the library loader sees it and loads from there?

Upvotes: 27

Views: 33651

Answers (5)

Ganesh Rohan
Ganesh Rohan

Reputation: 31

The below code is to set the LD_LIBRARY_PATH or any other environment variable paths that is required by the import modules.

if os.getenv('LD_LIBRARY_PATH')==None: 
    os.environ['LD_LIBRARY_PATH']='<PATH>'
    try:
        sys.stdout.flush()
        os.execl(sys.executable,sys.executable, *sys.argv)
    except OSError as e:
        print(e)
elif <path> not in os.getenv('LD_LIBRARY_PATH'):
    os.environ['LD_LIBRARY_PATH'] = ':'.join([os.getenv('LD_LIBRARY_PATH'),'<PATH>'])
    try:
        sys.stdout.flush()
        os.execl(sys.executable,sys.executable, *sys.argv)
    except OSError as e:
        print(e)

# import X

The function os.execl will replace the current process. In UNIX a new executable will be loaded into the current process. By having this code before the import of the 'X' module, now it will be looking for the files in the new path that was set.

More on execl

Upvotes: 0

cristi
cristi

Reputation: 2199

Based on the answer from Employed Russian, this is what works for me

oracle_libs = os.environ['ORACLE_HOME']+"/lib/"
rerun = True

if not 'LD_LIBRARY_PATH' in os.environ:
  os.environ['LD_LIBRARY_PATH'] = ":"+oracle_libs
elif not oracle_libs in os.environ.get('LD_LIBRARY_PATH'):
  os.environ['LD_LIBRARY_PATH'] += ":"+oracle_libs
else:
  rerun = False

if rerun:
  os.execve(os.path.realpath(__file__), sys.argv, os.environ)

Upvotes: 16

Employed Russian
Employed Russian

Reputation: 213596

The reason

os.environ["LD_LIBRARY_PATH"] = ...

doesn't work is simple: this environment variable controls behavior of the dynamic loader (ld-linux.so.2 on Linux, ld.so.1 on Solaris), but the loader only looks at LD_LIBRARY_PATH once at process startup. Changing the value of LD_LIBRARY_PATH in the current process after that point has no effect (just as the answer to this question says).

You do have some options:

A. If you know that you are going to need xyz.so from /some/path, and control the execution of python script from the start, then simply set LD_LIBRARY_PATH to your liking (after checking that it is not already so set), and re-execute yourself. This is what Java does.

B. You can import /some/path/xyz.so via its absolute path before importing x.so. When you then import x.so, the loader will discover that it has already loaded xyz.so, and will use the already loaded module instead of searching for it again.

C. If you build x.so yourself, you can add -Wl,-rpath=/some/path to its link line, and then importing x.so will cause the loader to look for dependent modules in /some/path.

Upvotes: 41

Aaron Watters
Aaron Watters

Reputation: 2846

In my experience trying to change the way the loader works for a running Python is very tricky; probably OS/version dependent; may not work. One work-around that might help in some circumstances is to launch a sub-process that changes the environment parameter using a shell script and then launch a new Python using the shell.

Upvotes: 0

Reputation:

well, the environment variables are stored in the dictionary os.environ, so if you want to change , you can do

os.environ["PATH"] = "/usr/bin"

Upvotes: -11

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