IntroductionLinux is known for its stability, flexibility,
and security. One of the primary functions of Linux is user management, which
helps administrators to control access to resources and their security. In an
era where the impact of technology is increasing, managing users is crucial for
a secure and organized environment.
Users
in Linux
To control the access and manage the security of
the operating system user plays a fundamental role in this regard. A user is an
entity (person, process or service) in Linux that logs in to the system and
performs specific tasks. Every user has a unique User ID (UID that is
associated with certain permissions, files and processes. A Linux system has several
user accounts for different purposes. At the top is the root user, which has
superuser privileges.
Types
of Users
Linux supports different types of users,
including system users, regular users, and the root user, which is the
superuser.
Root
User (Superuser)
The root user, with a UID of 0, has full control
over the system, including software installation, deletion, user management,
and editing system files.
System
Users (Service Accounts)
System users are created automatically by the
system during installation or when software packages are installed. System
users are designed to run services and applications in the background. Their
primary function is to manage and execute background services and processes
with secure and limited privileges. System
users like mysql, www, mail and bin etc.
System users have user IDs starting from 0 up to 1000. System users are
not logged in directly like a regular user and they lack login shell or
restricted shell access. System users enhance the security of the system as in
case of an attack, only that service is compromised rather than the whole
system.
Regular
Users
A regular user is non non-administrative
user account created for different purposes and sometimes assigned a specific
task to perform. Regular users have limited permissions as compared to the root
user and regular users can create files, run scripts and access their files and
directories. They are not able to install software without privileges and aren’t
able to modify the system files as well. Regular users are assigned user IDs
normally greater than 1000.
User
Configuration Files
·
/etc/passwd – store the information
about users
·
/etc/shadow – store user password hashes
readable only by root
·
/etc/group – users group information
·
/etc/login.def – default parameters of
user accounts
How
to create a User
The useradd command is used to create a user
in Linux. A user in Linux contains certain properties. First, create the user
with the useradd command and will see the user properties in detail.
#useradd
–u 1001 -d /home/seeklinux -s /bin/bash seeklinux
A Seeklinux user is created with uid
(-u) 1001, home directory (-d) and /bin/bash (-s) the default shell for Seeklinux.
To verify the newly created account commands is
#id
seeklinux
This will display the user ID, group ID
and group membership for the seeklinux user.
User
Account Properties
Every account in Linux contains
properties that define its characteristics and access privileges. Let's see
these properties in detail.
1. Username
Every
user account in Linux is assigned a unique username by which this user is
recognized, as the seeklinux username is seeklinux.
2. UID
Every
user account is assigned a unique UID and this UID is a numerical value as the UID
of seeklinux is 1001. UID is automatically assigned by the system to a user at
the time of creation, or you can specify by yourself when you create a user.
3. GID
GID
is group ID, the primary group ID of the user seeklinux is 1001.
4. Home Directory
Every
user has an associated home directory where personal files, documents and
settings reside. The home directory of seeklinux is /home/seeklinux.
5. Default Shell
The
default shell determines which interpreter the user will use after logging in.
This is the associated interactive environment of the user as SeekLinux’s
default shell is /bin/bash.
6. Password
Every
user should be secured by a strong password. A password is required to
authenticate and to interact with the system. The password should be according
to the password security policy.
7. Group
The
group membership determines the user's association with the group and access
privileges to the resources.
The user information is saved in the
/etc/passwd and to get this information, the command is
#grep
seeklinux /etc/passwd
/etc/passwd contains the following
fields.
Seeklinux
– seeklinux is the user that we created by the useradd command.
X
– Represents the encrypted password of the user account.
UID
– 1001 is UID. A unique identifier for a user account that is assigned by the system
automatically, or you can specify.
GID
– 1001 GID group ID for user account representing primary group membership of
user.
/home/seeklinux
– home directory of the user account.
/bin/bash
– the default shell for the user account
This is detailed information that is
stored in /etc/passwd about the users.
How
to set a user's Password
To create a user password, always follow
the password policies to set a strong password. Avoid setting a common password
that is easily guessable, especially in a production environment. To set the user
password command is
#sudo
passwd seeklinux
How
to Delete a User Account
To delete a user account, the command is
#usdo
userdel seeklinux
This will delete the user's home directory and
all associated files.
How
to Lock and Unlock a User Account
There are different ways to lock or
disable user accounts in Linux. We do this by using the following methods:
passwd, usermod and by modifying the /etc/shadow file.
Lock
user Using Passwd
To lock a user using the passwd command is
#sudo
passwd –l seeklinux
Disable
a User Account Using usermod
The usermod command is also a handy tool
to modify users. To disable a user, with usermod -L or --lock option is used.
#sudo
usermod -L seeklinux
How
to Set a User Shell to nologin
In this method, set the user shell to no
login. By doing this prevent the user from logging in to the system. Command is
#sudo
usermod –s /sbin/nologin seeklinux
The user will get this message when they try to
log in to the system.
Modify
the Shadow File (/etc/shadow)
A simple method to disable a user
account by modifying the /etc/shadow file. Open the shadow file with your
favorite editor and search the user that you want to disable. Put the ! Or * at
the start of that user to disable it.
#sudo
vi /etc/shadow
The user will get an authentication
failure error when try to log in to the system.
How
to unlock the User Account
To unlock the user account, the -U
option is used with the usermod command.
#sudo
usermod –U seeklinux
By
using passwd to unlock the user
#sudo
passwd –u seeklinux
How
to Check the User Status
To check the status of the user, whether it is
locked or unlocked, the command is
#sudo
passwd –S seeklinux
If the output shows the PS, it means the user is
unlocked; otherwise, it indicates that the LK user's status is locked.
Group
Management
Group management is a mandatory aspect in Linux
for system administration, providing efficient control over file and resource
access according to the user's role and granted permissions. Groups allow
membership to users in their respective groups.
Group
types
Primary
Group
This group is created automatically at the time
of user creation with the same name and ID. Every user has one primary group
associated with it.
Secondary
Group
Users belong to multiple or additional
groups for the grant of access to resources related to those groups. A user can
be a member of many secondary groups at a time.
/etc/group:
This is the main file for groups to
store information about all groups and their associated members with group IDs
(GIDs).
How
to Create a New Group
To create a new group, for example
developer, the command is
#sudo
groupadd developer
This group grants access and permissions
to all development-related resources.
To view the group detail that is created
with the name developer, go /etc/group file.
#cat
/etc/group
This command returns all group details,
and the newly created group will be at the bottom. You can sort the command to
see only the information of a specific group. Command is
#cat
/etc/group | grep developer
How
to Assign a User to a Group
Users can be assigned to a group after it
has been created. To assign the user to the group developer command is
#sudo
usermod -aG developer seeklinux
As Seeklinux is a member of the developer group
and he has access to the resources of this group.
How
to Delete a Group
To delete the group command is
#sudo
groupdel developer
That’s all about users and group
management. Keep visiting seeklinux for more updates and information.
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