On Unix, is there any way that one process can change another's environment variables (assuming they're all being run by the same user)? A general solution would be best, but if not, what about the specific case where one is a child of the other?
Edit: How about via gdb?
If your unix supports the /proc filesystem, then it's trivial to READ the env - you can read the environment, commandline, and many other attributes of any process you own that way. Changing it... Well, I can think of a way, but it's a BAD idea.
The more general case... I don't know, but I doubt there's a portable answer.
(Edited: my original answer assumed the OP wanted to READ the env, not change it)
Quoting Jerry Peek:
You can't teach an old dog new tricks.
The only thing you can do is to change the environment variable of the child process before starting it: it gets the copy of the parent environment, sorry.
See http://www.unix.com.ua/orelly/unix/upt/ch06_02.htm for details.
Just a comment on the answer about using /proc. Under linux /proc is supported but, it does not work, you cannot change the /proc/${pid}/environ file, even if you are root: it is absolutely read-only.
Not as far as I know. Really you're trying to communicate from one process to another which calls for one of the IPC methods (shared memory, semaphores, sockets, etc.). Having received data by one of these methods you could then set environment variables or perform other actions more directly.
Or get your process to update a config file for the new process and then either:
HTH.
cheers,
Rob
I could think of the rather contrived way to do that, and it will not work for arbitrary processes.
Suppose that you write your own shared library which implements 'char *getenv'. Then, you set up 'LD_PRELOAD' or 'LD_LIBRARY_PATH' env. vars so that both your processes are run with your shared library preloaded.
This way, you will essentially have a control over the code of the 'getenv' function. Then, you could do all sorts of nasty tricks. Your 'getenv' could consult external config file or SHM segment for alternate values of env vars. Or you could do regexp search/replace on the requested values. Or ...
I can't think of an easy way to do that for arbitrary running processes (even if you are root), short of rewriting dynamic linker (ld-linux.so).
Substantially, no. If you had sufficient privileges (root, or thereabouts) and poked around /dev/kmem (kernel memory), and you made changes to the process's environment, and if the process actually re-referenced the environment variable afterwards (that is, the process had not already taken a copy of the env var and was not using just that copy), then maybe, if you were lucky and clever, and the wind was blowing in the right direction, and the phase of the moon was correct, perhaps, you might achieve something.
Via gdb:
(gdb) attach process_id
(gdb) call putenv ("env_var_name=env_var_value")
(gdb) detach
This is quite a nasty hack and should only be done in the context of a debugging scenario, of course.
You probably can do it technically (see other answers), but it might not help you.
Most programs will expect that env vars cannot be changed from the outside after startup, hence most will probably just read the vars they are interested in at startup and initialize based on that. So changing them afterwards will not make a difference, since the program will never re-read them.
If you posted this as a concrete problem, you should probably take a different approach. If it was just out of curiosity: Nice question :-).
Not a direct answer but... Raymond Chen had a [Windows-based] rationale around this only the other day
Not an answer, but a follow-up question. I found this discussion when searching for a solution to the following: in Linux/Gnome, is there a way to change or add environment variable defined in .bash_profile, without the need to re-login? In Windows, I remember, it was possible to change a variable in "My Computer" properties, and then all programs which were launched after that, saw the new value.