17th October, 2020
-->The root user account is the equivalent of the administrator (or) Enterprise admin account in the windows world.
---> A system account is similar to a normal user account. The main difference is that system users normally don’t have a home directory and can’t log in the way normal users do
---> Normal users are the users created by the root user. They are normal users like Rahul, sara, Raju----- etc.
|System user||ftp, ssh, nobody||1-499||1-499||/var/ftp|
|Normal user||Visitor, sara||500-60,000||500-60,000||/home/user|
In Red Hat, Linux uses user private Group (UPG) schema. According to the UPG scheme, you create any user account, the user consists of the primary group with the same name and same ID.
---> For Example if a user is created with the name Raju, then a primary group of that user will be raju only.
(a) /etc/passwd: à This file maintains user-related information. Syn: <username> : <password> :<UID>: <GID> : <comments> : <Homedir> : <shell>
(b) /etc/shadow: à This file maintains user-related password information
Syn: <username> : <encrypted password> : <last passwd change> : <min>: <max> : <warn> : <inactive> : expires> : <not used>
A root user can change the password of self and any user in the system, there are no rules for root to assign a password. The root can assign any length of password either long or short, it can be an alphabet or numeric or both, on the whole, there is no limitation for root for assigning a password.
A normal user can change only its password. A valid password for a normal user should add here to the following rules.
To manage user accounts, you can use the following Linux commands
User add:- create user (or) system accounts.
Syn: Useradd [options] LOGIN
Ex: Create a user in linux
# cat /etc/passwd/grep raju
# useradd –u 555 –c “linux user” -d /opt/india –s /bin/sh india
#cat/etc passwd/ grep india
Tip:- As a good practice, you should provide a label or some description for each account; otherwise, after time, you will forget what it is for.
User mod:- Modifies user accounts.
Syn: User mod [options] LOGIN
Note:- All the options which are used with the user add command can be used and,
Ex: à Changing the name of the user
#usermod -l newname oldname
# Usermod -L Username
#usermod -U username
Note: When an account is locked it will show! (Exclamation mark) in /etc/shadow file.
Userdel: Removes a user or system account.
Syn: Userdel [options] LOGIN
Ex: #userdel username
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Passwd: Sets a password or resets a password for a user account
Syn: passwd [options] [LOGIN] -l à Locks a user’s account -u à Unlocks a user’s account
Ex: #passwd raju
Enables you to modify the parameters surrounding passwords (complexity, age, expiration)
Syn: Chage [options] user
Ex: Find the user’s password information #chage –l user
#chage –E 2013-03-28 raju
PWCK: verifies the consistency of passwords across database files.
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