Every user who has access to a Linux system needs a login and a password.
The numeric identifier are:
These identifiers are mapped to a name identifier known as username and group name in the /etc/passwd
The root login is the super admin user and as the UID 0
In order to create new logins, and modify or delete users, you must already be logged in as root.
The term root may refer to:
Each user:
The User Id can seen with:
id
uid=0(root) gid=0(root) groups=0(root)
if [ "${UID}" -eq 0 ]; then
echo "I'm root"
fi
The /etc/skel/ directory is for “skeleton” user files, which are used to populate a home directory when a user is first created. This directory can be modified to fit your needs. Modifications only effect new users and does not change anything for existing users.
The easiest way to manage users and groups is through the graphical applications:
The following table lists the available commands line for managing users and groups:
| Task | Command |
|---|---|
| Creating groups | Linux - Group (Gid) |
| Modifying groups | Linux - Group (Gid) |
| Deleting groups | Linux - Group (Gid) |
| Creating users | useradd |
| Modifying users | usermod |
| Deleting users | userdel |
| Change/set a password. | passwd |
| Switch to another user | su |
| Verification of the password, group, and associated shadow files | pwck: verify integrity of password files grpck |
| Conversion to shadow passwords and back to standard passwords | pwconv, pwunconv |
User names and primary groups are stored in /etc/passwd
Example:
cut -d: -f1 /etc/passwd
cat /etc/passwd | grep -i '.*vis'
oravis:x:502:502::/home/oravis:/bin/bash
applvis:x:503:502::/home/applvis:/bin/bash
the useradd command add a new user.
Options:
Example: To add a new user with
useradd -g oinstall -G dba -s /bin/shell -p xxxx -d /home/gerardnico -m gerardnico
- name: "Sqlline - Create the group"
group:
name: '{{ sqlline_group }}'
state: present
- name: "Sqlline - Create the user"
user:
name: '{{ sqlline_owner }}'
comment: Sqlline Installation user
shell: /bin/bash
state: present
group: '{{ sqlline_group }}'
password: {{ upassword | password_hash('sha512') }}
This command usermod modifies an existing user. You must use all the options in the same way as you create it.
Options:
Example: To add the group 'others' to the user gerardnico
usermod -G others gerardnico
To suppress a group for a user using the command line, you will have to list all the groups that you want the user in. For example if the user currently in group1,group2,group3,group4 and you want him out of group3 then
usermod -G group1,group2,group4 loginName
This command delete a a user,
Options:
Example: To remove the user 'gerardnico' and his home directory
[root@ebs121 /]# userdel -r gerardnico
bash: userdel: command not found
[root@ebs121 /]# /usr/sbin/userdel -r gerardnico