Disable and Enable users in Linux

Disable and Enable a user account in Linux :

 

Prevent user to access account / Prevent user to reach on shell prompt :

If you want to disable a user account in Linux, follow these steps.

if it is debian or ubuntu :

$ sudo usermod -s /usr/sbin/nologin username

if it is centos or fedora :

$ sudo usermod -s /sbin/nologin username

When you try to access disabled account, it says

This account is currently not available

Second Method : 
a) Open file /etc/passwd and search your username there.
b) If a line ends with /bin/bash, it means user can log in.
c) Change the text  /bin/bash  into /sbin/nologin (centos or fedora) or /usr/sbin/nologin (debian or ubuntu) for your username.
d) Save the file. Now User will not be able to log-in.

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Enable a User Account
Allow user to access account / Allow user to reach on shell prompt :

If you want to enable a user account in Linux, Run the command.

$ sudo chsh -s /bin/bash username

Second Method : 
a) Open file /etc/passwd and search your username there.
b) If a line ends with /sbin/nologin (centos or fedora) or /usr/sbin/nologin (debian or ubuntu), it means user can not log in.
c) Change the text /sbin/nologin (centos or fedora) or /usr/sbin/nologin (debian or ubuntu) into  /bin/bash  for your username.
d) Save the file. Now User will be able to log-in.

You can see the solution in the following video.