newgrp 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. The user will be prompted for a password if they do not have a password 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.
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