Question

I know that getenv() returns a value of specified environment variable of the current user, but my code requires root privileges so getenv() would only use the sudo environment variables. I also know that SUDO_USER tells which user is invoking sudo, which is the user environment I want use for getenv().

char* gnome_env_var = getenv("GDMSESSION"); //returns null as not found in sudo env
char* usr = getenv("SUDO_USER");

Is there a way I can get the value of an environment variable for the logged in user, not the sudo environment?

EDIT
Okay, so what I’m hearing is that the set of environment variables are unique to each process, not user and using sudo to invoke a process with root privileges calls execve which can create an entirely new set of environment variables for that process. So to rephrase, is there a way besides messing with the sudoers file, and within the current process, of finding the calling process’s environment variables?

I particularly need the GDMSession environment variable.

Answer 1

getenv doesn’t tell you about the environment variables of the current user, but the current process. Users are free to have as many environments as they want(and can create processes), for example with the export shell built-in. In every call to execve, the calling program is free to create an entirely new environment for the executed process.

Therefore, there is no way to get the environment variables of the user, or even those of the process executing sudo. Why do you want that anyways?

You can, however, configure sudo to keep some or all environment variables, via the keep_env and reset_env directives in /etc/sudoers.