Linux - User (Uid)

Every user who has access to a Linux system needs a login and a password. Each user must belong to a primary group and for security or access purposes can belong to several secondary groups.

The root login is the highest level and only certain individuals should have access to the root account.

The easiest way to manage users and groups is through the graphical applications:

• Red Hat Linux:
  • RHEL4 and higher: system-config-users
  • User Manager: redhat-config-users.
• SUSE Linux: yast or yast2

The following table lists the available commands line for managing users and groups:

• public user information: Linux - /etc/passwd (public user information)
• secure user information: Linux - /etc/shadow (Secure user information)

variable $UID: User ID number

The User Id can seen with:

• The id command:

id

uid=0(root) gid=0(root) groups=0(root)

• or the UID environment variable in Bash.

if [ "${UID}" -eq 0 ]; then
  echo "I'm root"
fi

• /home — Default location for users' home directories. For example, a user with the username foo has the home directory /home/foo
• /tmp — The reserved directory for all users to store temporary files. Files stored here are not permanent. A system process removes old files from this directory on a periodic basis. Do not write any files or directories that you want to keep here.

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.

User names and primary groups are stored in /etc/passwd

Example:

• all users

cut -d: -f1 /etc/passwd

• All users who contains the letters “vis” in their names (use the pipe symbol followed by the grep executable which has a pattern as input: '.*vis')

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:

• -d home directory
• -s starting program (shell)
• -p password
• -g (primary group assigned to the users)
• -G (Other groups the user belongs to)
• -m (Create the user's home directory)

Example: To add a new user with

• a primary group of oinstall
• a second group dba
• starting shell /bin/bash
• password of xxxx
• home directory of gerardnico
• create home directory
• a login name of gerardnico

useradd -g oinstall -G dba -s /bin/shell -p xxxx -d /home/gerardnico -m gerardnico

user module

- 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 modify an existing user. You must use all the options in the same way as you create it.

Options:

• -d home directory
• -s starting program (shell)
• -p password
• -g (primary group assigned to the users)
• -G (Other groups the user belongs to)

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:

• -r (remove home directory)

Example: To remove the user 'gerardnico' and his home directory

[[email protected] /]# userdel -r gerardnico
bash: userdel: command not found
[[email protected] /]# /usr/sbin/userdel -r gerardnico

See Linux - Password (User)

• Red Hat Linux 9: Red Hat Linux System Administration Primer - Chapter 6. Managing User Accounts and Resource Access
• Linux User Command