Bash interactive login shell vs interactive non-login shell

Here just talks interactive shells, not non-interactive ones.

I use Bash.

Design

One login shell at the top, and it spawns non-login shell. Non-login shells inherits most but *not* all settings from parent shell. So we should do heavy lifting work during login shell initialization, and left easy ones for non-login shell,  e.g. run df/uptime after login.

• What's the difference?

login shell:        when login via TTY or SSH

non-login shell: when run screen or bash

Startup files

Files are executed in this order. Taken from my VPS ubuntu image, your system might be different.

• login shell  (bash -l)

/etc/profile

    /etc/bash.bashrc  (sourced by /etc/profile)

~/.bash_profile

~/.bash_login

~/.profile  (will NOT run if .bash_profile or .bash_login exists)

    ~/.bashrc  (sourced by ~/.profile)

~/.bash_logout  (invoked when logout)

• non-login shell:  (bash)

/etc/bash.bashrc

~/.bashrc

Reference

• https://unix.stackexchange.com/questions/38175/difference-between-login-shell-and-non-login-shell
• https://unix.stackexchange.com/questions/324359/why-a-login-shell-over-a-non-login-shell
• https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html