Description

where are env variables stored linux ?

**Understanding Where Environment Variables Are Stored in Linux**

Environment variables are a core aspect of Linux and other Unix-based operating systems. They provide a way for the system and applications to access configuration information, such as the default editor, the list of directories to search for executables, and other settings that influence how a process behaves. But the question often arises: where exactly are these variables stored?

**In Process Memory**

The actual system and user environment variables are stored within the memory space of the process that starts up. Each time a new process starts, it inherits the environmental settings from its parent process. This means if you launch a script or a program from within a terminal session, the environment variables set in the terminal session are also available in the new process. The memory locations of these variables are not visible and readable like regular files on a drive; instead, they exist in the form of a key-value pair within the process’s memory space.

**In Configuration Files**

While we can’t directly point to a file where the environment variables are permanently stored, we can find configurations for them in several places on a Linux system:

1. **/etc/environment** – This system-wide file stores general environment variables. These will apply across the system when the system is booted up. Modifications to this file affect all users. Be sure to reboot or log out and back in after making changes for them to take effect.

2. **~/.bashrc and ~/.profile** – These are user-specific files that set environment variables. They are loaded when a login shell is initiated or when a user’s Bash terminal starts. Changes here impact only the user who owns these files and become effective when the terminal session is restarted.

3. **/etc/profile** – This file is used for system-wide definition of environment variables for all users. These definitions are applicable when the system starts and when a user logs in.

**Dynamic Access using /proc/[pid]/environ**

Interestingly, Linux provides a virtual file system called /proc. This pseudo-filesystem not only shows information about the kernel and the system but also about processes, such as environment variables. Each process has a corresponding /proc/[pid] directory, where [pid] is the process ID. Inside this directory, there’s an “environ” file that gives access to the current environment variables as seen by the process. You can view all the environment variables for a specific process by doing something like this in the terminal:

“`sh
cat /proc//environ
“`

Keep in mind that only the environment variables visible to that process will be listed, and they will also be in the raw format that a process needs, without any pretty text output. For example:

“`sh
LANG=fr_FR.UTF-8PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
“`

This reveals that even though environment variables appear as neatly named and accessible pieces of configuration data, their physical storage is relatively direct and can be quite technical to interact with for most users.

Understanding where Linux stores environment variables and how they can be permanently set gives users and system administrators more control over their Linux setup, allowing for customization that can influence system performance and behavior. Familiarizing yourself with the locations and methods of making changes can amplify the flexibility of your Linux infrastructure.