Where to declare environment variables?

What are correct places for:

1. Global environment variables meant to affect all users?
2. User-specific environment variables?

To add to sagarchalise's answer, I can summarize what the link suggests as appropriate places for settings.

For global settings, system-wide environment variables

• Use /etc/environment
• Don't use /etc/profile or /etc/bash.bashrc

From the page:

/etc/environment [...] is specifically meant for system-wide environment variable settings. It is not a script file, but rather consists of assignment expressions, one per line. Specifically, this file stores the system-wide locale and path settings.

Using /etc/profile is a very Unix-y way to go, but its functionality is greatly reduced under Ubuntu. It exists only to point to /etc/bash.bashrc and to collect entries from /etc/profile.d.

On my system, the only interesting entry entry in profile.d is /etc/profile.d/bash_completion.sh.

For local or per-user settings

The Ubuntu page recommends ~/.pam_environment, which is loaded by the PAM system when your session is started (TTY, GUI, SSH, etc.). It is the user-equivalent of /etc/environment and uses the same syntax. The link suggests alternatives if that doesn't work:

• ~/.profile for most shells. This file may also be applied to your GUI session by the display manager, but this need not be the case for all display managers or display servers (X11 vs Wayland) or sessions.

And bash-specific:

• ~/.bash_profile or ~./bash_login - If one of these exists, bash executes it instead of ~/.profile when bash is started as a login shell. Bash will prefer ~/.bash_profile to ~/.bash_login. [...] These files won't influence a graphical session by default."
• ~/.bashrc - "... may be the easiest place to set variables".

I think the community wiki page on environment variables will help you sort out