What is /etc/profile used for?
If you have been using Linux for a while you are probably familiar with the .profile or .bash_profile files in your home directory. These files are used to set environmental items for a users shell. Items such as umask, and variables such as PS1 or PATH. The /etc/profile file is not very different however it is used to set system wide environmental variables on users shells. The variables are sometimes the same ones that are in the .bash_profile, however this file is used to set an initial PATH or PS1 for all shell users of the system.
/etc/profile.d
In addition to the setting environmental items the /etc/profile will execute the scripts within /etc/profile.d/*.sh. If you plan on setting your own system wide environmental variables it is recommended to place your configuration in a shell script within /etc/profile.d.
What is /etc/bashrc used for?
Like .bash_profile you will also commonly see a .bashrc file in your home directory. This file is meant for setting command aliases and functions used by bash shell users.
Just like the /etc/profile is the system wide version of .bash_profile. The /etc/bashrc for Red Hat and /etc/bash.bashrc in Ubuntu is the system wide version of .bashrc.
Interestingly enough in the Red Hat implementation the /etc/bashrc also executes the shell scripts within /etc/profile.d but only if the users shell is a Interactive Shell (aka Login Shell)
When are these files used?
The difference between when these two files are executed are dependent on the type of login being performed. In Linux you can have two types of login shells, Interactive Shells and Non-Interactive Shells. An Interactive shell is used where a user can interact with the shell, i.e. your typical bash prompt. Whereas a non-Interactive shell is used when a user cannot interact with the shell, i.e. a bash scripts execution. The difference is simple, the /etc/profile is executed only for interactive shells and the /etc/bashrc is executed for both interactive and non-interactive shells. In fact in Ubuntu the /etc/profile calls the /etc/bashrc directly. Interactive Shell vs Non-Interactive Shell To show an example of an interactive shell vs a non-interactive shell I will add a variable into both /etc/profile and /etc/bash.bashrc on my Ubuntu system.
/etc/profile
#grep TEST /etc/profile export TESTPROFILE=1
/etc/bash.bashrc
#grep TEST /etc/bash.bashrc export TESTBASHRC=1
Interactive Shell
The below example is showing an interactive shell, in this case both the /etc/profile and /etc/bash.bashrc was executed.
#su -
#env | grep TEST
TESTBASHRC=1
TESTPROFILE=1
Non-Interactive Shell
In this example we are running a command through SSH that is non-interactive; because this is a non-interactive shell only the /etc/bash.bashrc file is executed.
#ssh localhost "env | grep TEST"
root@localhost's password:
TESTBASHRC=1