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Full Discussion: newgrp in a script
Top Forums UNIX for Dummies Questions & Answers newgrp in a script Post 46100 by Perderabo on Thursday 8th of January 2004 10:19:28 AM
Old 01-08-2004
For newgrp to work, the user must be listed in the group entry. But if the user is listed in the group entry, the login program will make the user a member of the group at login time. Thus newgrp is a no-op. I just tested this on Solaris. Try it yourself:
groups
newgrp somegrp
groups
This might be useful is a user was recently added to a group, I suppose. But the user some just sign off and on again. Or exec login or something.

Or you could be using group passwords. But there is no tool to assign them. Did you write one or something? There is no equivalent of /etc/shadow for group passwords. You would be leaving the encrypted password in plain sight. The manpage for newgrp warns against using group passwords. Group passwords were deprecated over a quarter of a century ago.

Doing what you want is trivial. I can't imagine how your got it work with newgrp but arranged for it to not work without newgroup. In fact, I strongly suspect that you are finished, but don't know it.

Everyone is in groupa. A few people are in groupb. Now you do:
chgrp groupb somefile
chmod 464 somefile

Now everyone can read somefile. Those folks (and only those folks) in groupb can write it. And all the groupb people need to do is logon. Forget about newgrp. It is that simple.
 

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LEARN ABOUT CENTOS

newgrp

NEWGRP(1)							   User Commands							 NEWGRP(1)

NAME

       newgrp - log in to a new group

SYNOPSIS

       newgrp [-] [group]

DESCRIPTION

       The newgrp command is used to change the current group ID during a login session. If the optional - flag is given, the user's environment
       will be reinitialized as though the user had logged in, otherwise the current environment, including current working directory, remains
       unchanged.

       newgrp changes the current real group ID to the named group, or to the default group listed in /etc/passwd if no group name is given.
       newgrp also tries to add the group to the user groupset. If not root, the user will be prompted for a password if she does not have a
       password (in /etc/shadow if this user has an entry in the shadowed password file, or in /etc/passwd otherwise) and the group does, or if
       the user is not listed as a member and the group has a password. The user will be denied access if the group password is empty and the user
       is not listed as a member.

       If there is an entry for this group in /etc/gshadow, then the list of members and the password of this group will be taken from this file,
       otherwise, the entry in /etc/group is considered.

CONFIGURATION

       The following configuration variables in /etc/login.defs change the behavior of this tool:

       SYSLOG_SG_ENAB (boolean)
	   Enable "syslog" logging of sg activity.

FILES

       /etc/passwd
	   User account information.

       /etc/shadow
	   Secure user account information.

       /etc/group
	   Group account information.

       /etc/gshadow
	   Secure group account information.

SEE ALSO

       id(1), login(1), su(1), sg(1), gpasswd(1), group(5), gshadow(5).

shadow-utils 4.1.5.1						    05/25/2012								 NEWGRP(1)
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