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Full Discussion: Non-interactive & non-login shell environment?
Top Forums UNIX for Beginners Questions & Answers Non-interactive & non-login shell environment? Post 303007484 by MadeInGermany on Friday 17th of November 2017 05:27:04 AM
Old 11-17-2017
The "Linux" kernel handles the scheduling/multitasking and all the I/O, and it knows what an UIDs/owner is.
But it does not know what a shell is, and does not know that a UID is stored in a passwd file.
Nevertheless the kernel handle many atomic operations. Its API towards userland is in man page section 2; in Linux you can list them with:
Code:
man -k . | grep '(2)'

The userland is all the processes. The shell is a normal process. A lot userland code is stored in shared libraries, so the processes simply load the libraries and stay small. The ps -ef command also lists some kernel threads and assignes the PID 0, while the real processes in userland have PID 1 and higher.

The criteria interactive/non-interactive and login/non-login is a matter of the shell, or of the process that invokes it. You can read more of it in the man page
Code:
man sh
man bash

The invocation of a new process is done via a couple of the kernel API functions, basically fork() and exec().
 

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LEARN ABOUT OPENDARWIN

chsh

CHSH(1)                                                            User Commands                                                           CHSH(1)

NAME

       chsh - change login shell

SYNOPSIS

       chsh [options] [LOGIN]

DESCRIPTION

       The chsh command changes the user login shell. This determines the name of the user's initial login command. A normal user may only change
       the login shell for her own account; the superuser may change the login shell for any account.

OPTIONS

       The options which apply to the chsh command are:

       -h, --help
           Display help message and exit.

       -R, --root CHROOT_DIR
           Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.

       -s, --shell SHELL
           The name of the user's new login shell. Setting this field to blank causes the system to select the default login shell.

       If the -s option is not selected, chsh operates in an interactive fashion, prompting the user with the current login shell. Enter the new
       value to change the shell, or leave the line blank to use the current one. The current shell is displayed between a pair of [ ] marks.

NOTE

       The only restriction placed on the login shell is that the command name must be listed in /etc/shells, unless the invoker is the superuser,
       and then any value may be added. An account with a restricted login shell may not change her login shell. For this reason, placing /bin/rsh
       in /etc/shells is discouraged since accidentally changing to a restricted shell would prevent the user from ever changing her login shell
       back to its original value.

FILES

       /etc/passwd
           User account information.

       /etc/shells
           List of valid login shells.

       /etc/login.defs
           Shadow password suite configuration.

SEE ALSO

       chfn(1), login.defs(5), passwd(5).

shadow-utils 4.5                                                    01/25/2018                                                             CHSH(1)
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