Arch Linux

andonuts_388

Member

Registered: 2010-05-23

Posts: 15

What is a login shell

I was following the Archwiki guide on colouring the bash prompt and found that if I open gnome-terminal and use 'su root' I get a colourised prompt but if I used 'su - root' which I found out to be the same as 'su -l root' then I didn't.

Some further research told me that -l makes the shell a login shell but I still don't really understand what that is or how it is any different. Can anyone enlighten me? Thankyou.

fsckd

Forum Fellow

Registered: 2009-06-15

Posts: 4,173

Re: What is a login shell

A shell will produce a different environment when started as a login shell than when not. You should read your shell's manpage for a description of the process. Assuming you are using bash as your shell, you would want to read the section titled INVOCATION.

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ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,791

Re: What is a login shell

I may be mistaken, but I believe the major difference is that when you su using a login shell, all of the login scripts for that shell run when it is instantiated.  On my system, that includes changing to the new user's $HOME. 

Without the -l, the system changes to the new user, but things like the CWD and PATH remain unchanged

For the purposes of system administration where you are switching to root, I don't think it matters which you use -- unless you do or don't what to change the environment.

[edit: added a missing verb.  Note to self: Don't post when you are tired]

Last edited by ewaller (2010-05-29 14:41:48)

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andonuts_388

Member

Registered: 2010-05-23

Posts: 15

Re: What is a login shell

So in normal use, there's no issue using su -l or just su?

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,791

Re: What is a login shell

So in normal use, there's no issue using su -l or just su?

I would say that is true.  In practice, I almost always use sudo.  The only time I actually change to root is if I'm trying to write to a pipe to a second program which also needs root privilege.  I am too lazy to figure out the correct incarnation for that.  I don't believe I have ever used su -l

edit: fixed typo

Last edited by ewaller (2010-05-29 16:08:12)

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cesura

Package Maintainer (PM)

From: Tallinn, Estonia

Registered: 2010-01-23

Posts: 1,867

Re: What is a login shell

In a nice way to put it, without -l, it will just change users. With it, it will take that user to their home directory and use their config files.

Hope I was right on that one

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hbekel

Member

Registered: 2008-10-04

Posts: 311

Re: What is a login shell

The common solution is to source ~/.bashrc from ~/.profile, e.g. add

. $HOME/.bashrc

to ~/.profile

So that your bashrc gets sourced regardless of whether it's a login shell or not.

andonuts_388

Member

Registered: 2010-05-23

Posts: 15

Re: What is a login shell

Thankyou all