Login Files

Thanks to flowbok's excellent article I have a seemingly very good idea of how start up files are handled on the various systems I am on.

But I need a bit more concrete example set. So, this is my attempt at those examples.

flowbok's repo which contains his basic startup files.

Setup

You will need access to a system to which you have root access in order to fully test these logins.

• Create a test user (I used 'testloginfiles'). How to do that on your system is beyond the scope of this project.

• Modify /etc/profile and add the following as the first executable line (replacing 'testloginfiles' with the username you created).

  test $USER == 'testloginfiles' && echo "/etc/profile (-: $-) ($(shopt login_shell))"

• Modify /etc/bash.bashrc and add the following as the first executable line (replace 'testloginfiles' with the username you created).

  [[ $USER == 'testloginfiles' ]] && echo "/etc/bash.bashrc (-: $-) ($(shopt login_shell))"

• Create .bash_profile, .bashrc, .profile and test.sh in your users home directory. They should each contain only one line, replacing the filename for each, as follows. Make sure test.sh is executable.

  echo "<filename> (-: $-) ($(shopt login_shell))"

System Information

These tests were run in an Arch Linux environment.

Summary

login (from terminal)
ssh user@host
sudo -i -u user
su --login user
su -l user
su - user

• interactive
• login shell
• /etc/profile
• /etc/bash.bashrc
• user's .bash_profile

ssh user@host command
ssh user@host -t command
su -c command user
sudo -u user command

• non-interactive
• no login shell
• no startup files executed

su user

• interactive
• no login shell
• /etc/bash.bashrc
• user's .bashrc

sudo -i -u user command
su --login user -c command
su -l user -c command
su - user -c command

• non-interactive
• login shell
• /etc/profile
• user's .bash_profile

Note: After user's .bash_profile is executed it appears that login_shell is turned off for the sudo command.

Startup Methods

There are many, many ... many login methods. I will list them here as I discover them and list the results as I discover the results.

Terminal

login (from terminal)

Shell set to /bin/bash

sweetums login: testloginfiles
Password:
Last login: Thu May  2 09:45:06 on tty2
/etc/profile (-: himBH) (login_shell        on)
/etc/bash.bashrc (-: himBH) (login_shell    on)
/home/testloginfiles/.bash_profile (-: himBH) (login_shell      on)
[testloginfiles@sweetums ~]$

Shell set to /bin/sh

Logging in from the terminal produces:

sweetums login: testloginfiles
Password:
Last login: Thu May  2 09:45:06 on tty2
/etc/profile (-: himBH) (login_shell        on)
/etc/bash.bashrc (-: himBH) (login_shell    on)
/home/testloginfiles/.bash_profile (-: himBH) (login_shell      on)
[testloginfiles@sweetums ~]$

ssh

ssh user@host

This command gives us the same results as a terminal login:

$ ssh testloginfiles@localhost
testloginfiles@localhost's password:
Last login: Thu May  2 09:46:24 2019
/etc/profile (-: himBH) (login_shell            on)
/etc/bash.bashrc (-: himBH) (login_shell        on)
/home/testloginfiles/.bash_profile (-: himBH) (login_shell      on)
[testloginfiles@sweetums ~]$

ssh user@host command

This runs the command (which must be a fully qualified path to the command) and returns to the caller.

$ ssh testloginfiles@localhost /home/testloginfiles/test.sh
/home/testloginfiles/test.sh (-: hB) (login_shell       off)

ssh user@host -t command

This runs the command (which must be a fully qualified path to the command) and returns to the caller.

ssh -t testloginfiles@localhost /home/testloginfiles/test.sh
/home/testloginfiles/test.sh (-: hB) (login_shell       off)
Shared connection to localhost closed.

su

su user

This method (partially?) preserves the calling environment. The harleypig at the end means we're still in the calling users home directory.

From the su man page:

For backward compatibility, su defaults to not change the current directory and to only set the environment variables HOME and SHELL (plus USER and LOGNAME if the target user is not root).

This means that your existing environment will be accessible from user's environment. This is a possible security risk, so you might want to keep it in mind when using this method.

$ su testloginfiles
Password:
/etc/bash.bashrc (-: himBH) (login_shell        off)
/home/testloginfiles/.bashrc (-: himBH) (login_shell            off)
[testloginfiles@sweetums harleypig]$

su -c command user

This method does not have the same problem as above.

su -c /home/testloginfiles/test.sh testloginfiles
Password:
/home/testloginfiles/test.sh (-: hB) (login_shell       off)

su - user

su -l user

su --login user

These methods gives us the same result as a terminal login.

$ su - testloginfiles
Password:
/etc/profile (-: himBH) (login_shell            on)
/etc/bash.bashrc (-: himBH) (login_shell        on)
/home/testloginfiles/.bash_profile (-: himBH) (login_shell      on)
[testloginfiles@sweetums ~]$

su - user -c command

su -l user -c command

su --login user -c command

These methods gives us these results.

$ su - testloginfiles -c /home/testloginfiles/test.sh
Password:
/etc/profile (-: hBc) (login_shell      on)
/home/testloginfiles/.bash_profile (-: hBc) (login_shell        on)
/home/testloginfiles/test.sh (-: hB) (login_shell       off)

Notes

There is not supposed to be a difference between -, -l and --login but the man page for su warns against using the shortcuts, so we should probably test all three options.

If the need for the remaining options appears I'll add them. Pull requests will be considered as well.

test options --pty, --preserve-environment, --shell, --session-command?

sudo

sudo -i -u user

Same as a terminal login.

$ sudo -i -u testloginfiles
/etc/profile (-: himBH) (login_shell            on)
/etc/bash.bashrc (-: himBH) (login_shell        on)
/home/testloginfiles/.bash_profile (-: himBH) (login_shell      on)
[testloginfiles@sweetums ~]$

sudo -u user command

$ sudo -u testloginfiles /home/testloginfiles/test.sh
/home/testloginfiles/test.sh (-: hB) (login_shell       off)

sudo -i -u user command

Not sure why this is, but login_shell is turned off after .bash_profile is executed.

$ sudo -i -u testloginfiles /home/testloginfiles/test.sh
/etc/profile (-: hBc) (login_shell      on)
/home/testloginfiles/.bash_profile (-: hBc) (login_shell        on)
/home/testloginfiles/test.sh (-: hB) (login_shell       off)

TBD

cron, csh, ksh, tcsh, zsh, sh

Start bash with $BASH_ENV set

Resources

https://unix.stackexchange.com/questions/382984/the-zeroth-argument-to-a-command-executed-by-exec https://unix.stackexchange.com/questions/435625/does-a-noninteractive-login-shell-execute-profile-or-a-file-whose-name-is/435626 https://unix.stackexchange.com/questions/tagged/bash+configuration https://unix.stackexchange.com/questions/435744/how-can-we-start-bash-with-the-first-character-of-argument-zero-being