What is exact purpose of login versus non-login bash shells?

[mendicant]

Hi,

I hope I am posting this question in the right place.

During the set up for Linux From Scratch I was directed to use a login shell as opposed to a non-login shell. I have spent a fair amount of time trying to figure out the exact purpose for one as opposed to the other. I have found a great deal of information on how to invoke the two types of shells as well as the scripts that are run by each of them. What is not clear to me is why one would use one of these shells as opposed to the other. Now that I have spent so much time trying to track down an answer I would greatly appreciate any details any of you out there could give me.

Thanks in advance, M.

[LinuxTom]

To the best of my understanding the login shell invokes... (Feel free to correct me if I am wrong)

/etc/bashrc
/etc/profile
~/.bashrc
~/.bash_profile

Whereas a non-login shell only invokes...

/etc/bashrc
~/.bashrc

The login shell essentially sets up the user configured variables (and system variables) then executes the secondary (non-login) shell where you would execute your programs. As to why one would use one type of login over another I don't really know; I have always used the login shell when using su.

[sonoran]

From the bash info page:

"When Bash is invoked as an interactive login shell, or as a
non-interactive shell with the `--login' option, it first reads and
executes commands from the file `/etc/profile', if that file exists.
After reading that file, it looks for `~/.bash_profile',
`~/.bash_login', and `~/.profile', in that order, and reads and
executes commands from the first one that exists and is readable.

When a login shell exits, Bash reads and executes commands from the
file `~/.bash_logout', if it exists."

"When an interactive shell that is not a login shell is started, Bash
reads and executes commands from `~/.bashrc', if that file exists."

There's a lot more in man bash and info bash if you really want to dig into it.

[mendicant]

Thanks for the feedback.

LinuxTom: It would make sense in the context of what I was doing i.e. setting up an unprivileged user to safely begin the building of a Linux From Scratch system. If the login shell is used as you say to "essentially set(s) up the user configured variables (and system variables) then execute(s) the secondary (non-login) shell where you would execute your programs" why would you then always use the login shell as root? I'm not questioning whether it works or not for you - obviously it does. Are you saying that by bringing up a login shell you end up in a non-login shell anyway? My goal with Linux From Scratch is to gain a more complete understanding of the basics of the Linux OS. I find this sort of thing very confusing.

Again I appreciate your feedback, M.

[LinuxTom]

From my understanding (at least as it applies to the su command) if you use a login shell (ie: su - username) the environment is set up, then the secondary shell (non-login) is loaded for user interaction. The documentation on all of this stuff is massive, but sometimes hard to follow in typical Linux fashion.