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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 CENTOS

chsh

CHSH(1) 							   User Commands							   CHSH(1)

NAME

       chsh - change your login shell

SYNOPSIS

       chsh [-s shell] [-l] [-u] [-v] [username]

DESCRIPTION

       chsh is used to change your login shell.  If a shell is not given on the command line, chsh prompts for one.

       chsh is used to change local entries only. Use ypchsh, lchsh or any other implementation for non-local entries.

OPTIONS

       -s, --shell shell
	      Specify your login shell.

       -l, --list-shells
	      Print the list of shells listed in /etc/shells and exit.

       -u, --help
	      Print a usage message and exit.

       -v, --version
	      Print version information and exit.

VALID SHELLS

       chsh  will  accept  the full pathname of any executable file on the system.  However, it will issue a warning if the shell is not listed in
       the /etc/shells file.  On the other hand, it can also be configured such that it will only accept shells listed in this	file,  unless  you
       are root.

EXIT STATUS

       Returns 0 if operation was successful, 1 if operation failed or command syntax was not valid.

SEE ALSO

       login(1), passwd(5), shells(5)

AUTHOR

       Salvatore Valente <svalente@mit.edu>

AVAILABILITY

       The chsh command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

util-linux							     July 2009								   CHSH(1)
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