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Full Discussion: export vs env vs set commands
Operating Systems Solaris export vs env vs set commands Post 302531838 by bartus11 on Saturday 18th of June 2011 07:34:32 AM
Old 06-18-2011
Quote:
Originally Posted by presul
What does it mean to make a value of variable known to a sub-shell ?
Code:
[root@linux ~]# x=5                       <= here variable is set without export command
[root@linux ~]# echo $x
5
[root@linux ~]# bash                      <= subshell creation
[root@linux ~]# echo $x                   <= subshell doesnt know $x variable value

[root@linux ~]# exit                      <= exit from subshell
exit
[root@linux ~]# echo $x                   <= parent shell still knows $x variable
5
[root@linux ~]# export x=5                <= specify $x variable value using export command
[root@linux ~]# echo $x                   <= parent shell doesn't see any difference from the first declaration
5
[root@linux ~]# bash                      <= create subshell again
[root@linux ~]# echo $x                   <= now the subshell knows $x variable value
5
[root@linux ~]#

 

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LEARN ABOUT CENTOS

sulogin

SULOGIN(8)						       System Administration							SULOGIN(8)

NAME

       sulogin - Single-user login

SYNOPSIS

       sulogin [options] [tty]

DESCRIPTION

       sulogin is invoked by init when the system goes into single user mode.

       The user is prompted:

	    Give root password for system maintenance
	    (or type Control-D for normal startup):

       sulogin	will  be  connected  to  the  current terminal, or to the optional tty device that can be specified on the command line (typically
       /dev/console).

       After the user exits the single-user shell or presses control-D at the prompt, the system will continue to boot.

OPTIONS

       -e, --force
	      If the default method of obtaining the root password via getpwnam(3)  from  the  system  fails,  manually  examine  /etc/passwd  and
	      /etc/shadow to get the password.	If they are damaged or nonexistent, sulogin will start a root shell without asking for a password.

	      Only use the -e option if you are sure the console is physically protected against unauthorized access.

       -p, --login-shell
	      Specifying this option causes sulogin to start the shell process as a login shell.

       -t, --timeout seconds
	      Specify the maximum amount of time to wait for user input.  By default, sulogin will wait forever.

       -h, --help
	      Print a help message.

       -V, --version
	      Output version.

ENVIRONMENT VARIABLES

       sulogin looks for the environment variable SUSHELL or sushell to determine what shell to start.	If the environment variable is not set, it
       will try to execute root's shell from /etc/passwd.  If that fails it will fall back to /bin/sh.

AUTHOR

       sulogin was written by Miquel van Smoorenburg for sysvinit and later ported to util-linux by Dave Reisner and Karel Zak.

AVAILABILITY

       The sulogin command is part of the util-linux package and is available  from  Linux  Kernel  Archive  <ftp://ftp.kernel.org/pub/linux/utils
       /util-linux/>.

util-linux							     Jul 2012								SULOGIN(8)
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