Adding a User & Groups in CentOS [StartupCTO]

Last Updated: 08 Jul 2023

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Author: 111.225.149.195

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= Adding a User & Groups in CentOS =

If you're using command line CentOS, adding a user is a bit complicated. FreeBSD has a nice command line script (''adduser''), but in CentOS:
<code>
 useradd -d /home/bobsmith -s /bin/bash -c "Bob Smith" bobsmith
 passwd bobsmith
</code>
 
If you want the user account to be created, but not let the user login via the command line, set the shell to ''/bin/false''. If you want to prevent them from logging in at all (even via email, etc., set it to ''/sbin/nologin'')
== Adding Groups ==

If you want to add a group, the easiest way is to manually modify the ''/etc/group'' file, and copy one of the existing entries. You comma-delimit usernames when adding users to a group; e.g.:
<code>
users:x:100:dordal,bsmith,bjones
</code>
== Common Groups ==

By default on CentOS, every user is added to a group of their own name. In other words, the user **dordal** is added to the group **dordal**, as the default group. When a user creates files, its with a ''umask'' of ''002'', meaning read/write access for the user + group, and read access for the world. (See ''/etc/bashrc'' for where this is set.)

This makes for fairly fine-grained permissions, effectively meaning that any file the user creates is writable by them and only them. That works, but in many cases you may want to have a whole bunch of people be able to write to the same set of files (e.g. everyone in the marketing department can write to a common data store). In this case, you want to put them all in the same group (e.g. 'marketing'), and then:
<code>chown -R :marketing myfiles</code>
Then you want to say:
<code>chmod -R g+s myfiles</code>
which  sets the permissions so that any //new// files are created with the same group as the parent folder (e.g. 'marketing'), rather than the group of the user (e.g. 'dordal').

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