Manually Add a User Without Tools Like useradd and adduser in Linux

Last Updated : 29 Feb, 2024

Adding a user manually in Linux without using tools like useradd or adduser involves modifying system files directly. This method is not recommended for regular use, as it requires careful editing of system files and can lead to errors if not done correctly. However, in some situations, such as when these tools are not available or not working, it can be useful to know how to add a user manually. In this article, we will explain how to manually add a user in Linux

Manually Add a User Without Tools Like useradd and adduser in Linux

This article provides a step by step guide to add user manually, without using “useradd” or “adduser”.

useradd: The useradd command in Linux is a tool used to add or create new user on the system. It is mainly used to create user, configuring the login shell of the user.
adduser: It is also a user management tool but with a prominent management utility. It is often found in Debian-based distribution such as Ubuntu, Kali Linux, and its derivatives.

It is used to add user simply and it also provides more interactive features such as it adds user with a communal nature such as notifying user with questions and suggestions to assist and configure new user accounts, it also add default configuration and used with default values using various attributes.

Table of Content

Limitations of useradd and adduser tools:
File System changes after creation of new user.
Steps to add user manually in Linux based Operating System
Manually Add a User Without Tools Like useradd and adduser in Linux – FAQs

Limitations of useradd and adduser tools:

Permissions and Security: Both tools useradd and adduser do not sett up permissions for the user’s home directory or any other resources.
Additional Configuration: For advanced user management tasks, such as setting up user groups, secondary groups, or setting up custom home directory, user might need to use additional commands or do the manual configuration after using tools like adduser or useradd.
Lack of Validation: Both tools do not necessarily validate all parameters, so incorrect usage might lead to unexpected results or errors.

File System changes after creation of new user.

The /etc/passwd file is updated with new entry of user.
The /etc/shadow file is update with entry of our new user, containing encrypted password information.
The new home directory is created in /home directory and the contents of /skel directory is copied in the home directory of new user, which provides default configuration and file directories for the user.
The change of permission and ownership of user’s home directory is made to ensure the new user has significant access.

Steps to add user manually in Linux based Operating System

Step 1: Creating User

To create a user manually in linux based OS in this scenario “Ubuntu”, we will edit or add a line in passwd file located in etc directory.

‘/etc/passwd’, the passwd file consist of user information includes seven columns separated by colons.

Syntax:

Username:password:user-id:group-id:user-info:home-directory:login-shell

Username: It is the username of the user, it should be between 1 to 32 characters long. Only (‘_’, ‘-’, ‘.’ ) special characters are allowed and cannot contain any spaces, It also should start with a letter, and they are also case-sensitive.
Password: It is stored in hashed form, where ‘x’ is the hash stored in shadow file i.e. located in “etc/shadow”.
User-id: It is a unique numeric value assigned to uniquely identify the used, it should not be repeated or be same as other user.
Group-id: It is also unique numeric value representing group of the user if you want to create the user in the same group you can assign the value of the old group.
User-info: In this field the extra info related to user is present separated by comma.
Home-directory: It is the absolute path of the home directory of user.
Login-shell: It is the path of shell.

etc_passwd

Step2: Creating Group

As we created group-id for our user in ‘/etc/passwd’ its time to add a group which coordinates with our group-id.

To create a group we will edit the group file which is located in /etc directory i.e. “/etc/group”.

It is similar to the passwd file but contains four columns separated by colons.

Syntax:

Group-name:password:group-id:

Group Name: It must be between 1 to 32 characters long.
Password: It is stored in hashed form, where ‘x’ is the hash stored in shadow file i.e. located in “etc/shadow”.
group-id: Same numeric unique group-id.

The fourth column is left empty, it contains list of usernames separated by commas.
etc_group

Step3: Home Directory

To create a home directory we will use copy command “cp” with -r or recursive attribute and our skeleton directory i.e. “/etc/skel”.

Syntax:

cp --recursive /etc/skel /home/username

roothdir

Replace username with the actual username to create a home directory.

Step4: Changing ownership

The default permission of newly created user is set to root i.e. the “home” of our user belongs to root, to change the permission and the ownership of our user, we will use “chmod“ and “chown“.

chown [options] Owner:Group file

chown: The chown is a command line tool stands for change owner, it is used to change the owner and group of files and directories.
options: In our case we will use “-r” recursive flag with chown to change the ownership of the “home” of our new user.
Owner: In place of owner we will assign new user’s username or its unique numeric ID.
Group: In place of group we will assign group of our new user or its unique numeric ID.
File: In place of file we will assign the path of our “home” as we have to change the permission of home of our user.

demo-hdir

Step5: Changing permission

To change the permission of our user’s home directory we will use chmod with recursive option and mode.

chmod option mode file

chmod: The chmod is a command line tool stands for change mode, it is used to change the permission of files and directories. It allows user to set permission who can read, write and execute the file or directory in the system.
option: In our case we will use “-r” recursive flag with chown to change the mode of the “home” of our new user.
mode: It specifies the permission to be changed, and is represented by symbolic or octal representation.
file: It is simply the path of the file or directory whose permission we have to change in our case it is “/home/username“.

perm_demo

Step6: Creating Password

To create password for our newly created user we will use a command line utility “passwd“.

Syntax:

passwd username

replace the username with actual username.

passwd

Step7: whoami

To confirm the successful creation of our new user we will login to our new user and confirm the creation of user using “whoami” command.

$ su demouser
Password:
$ whoami
demouser

su-demouser

whoami

Permissions and ownerships

We can also manage the permission and ownership of our user’s home directory for example if we want give read, write and execute permission to user and no permission to group and others, we will assign mode 700 in step 5. We can change and grant permission as per our requirements for user, group and others. We just have to keep in mind that each digit represents the combination of read (4), write (2), and execute (1) permissions and granting permission to user, group and other respectively.

We can also change the ownership of the user, for example we can assign different group to our user’s home directory in step 4

Example:

chown  --recursive demouser:group1 /home/demouser

Security consideration

When adding user manually we should consider the following secure steps to protect against potential vulnerabilities:

Creating a secure password is a first and most common step to make our system more secure.
Assigning appropriate privileges to the new user account is a good step as it limits the use to access the whole system and allows them to perform their intended tasks.
Assuring that the user have the permission of read, write and execute for their own home directory and the access of other’s home directory is denied.
Monitoring user’s activity on the system and maintaining detailed logs of user actions is also a good step towards security as it helps to detect suspicious behavior or unauthorized access attempts.