Error 530 : Login incorrect

There can be several reasons of this error. Please try following solutions.

1) If you are using vsftpd, check this attribute in your vsftpd.conf
     local_enable=YES
     Value of the attribute should be YES otherwise you will not be able to log-in as a user. Restart the vsftpd after any change in configuration file.

Path of the vsftpd.conf :
/etc/vsftpd.conf  (if You are using debian or ubuntu)
/etc/vsftpd/vsftpd.conf (if you are using centOS, RHEL or fedora)

2) Check your username in the file ftpusers.
If your username is in the list, you can't log into your ftp account. This file contains the list of usernames who should not log-in. Remove your username from the list and save the file. Now try to log into your ftp account.

Path of the the file ftpusers :
/etc/ftpusers  (if You are using debian or ubuntu)
/etc/vsftpd/ftpusers (if you are using centOS, RHEL or fedora)

3) Open file /etc/passwd and search your username there. If your username's line ends with /sbin/nologin (centos or RHEL) or /usr/sbin/nologin (debian or ubuntu), it means user can not log in. Change the text /sbin/nologin (centos or RHEL) or /usr/sbin/nologin (debian or ubuntu) into  /bin/bash. Save the file. Now User will be able to log-in.
Name of the shell should be defined for your username in the file /etc/passwd as well as it should be in the list in file /etc/shells.

4) User should not be locked by root. If user is locked, use following command to unlock. Now try to log-in.

$ sudo passwd -u username

5) If you are using CentOS or RHEL, the port 21 should be defined in the file /etc/sysconfig/iptables. Add following line in the file and restart iptables.
-A INPUT -m state --state NEW -m tcp -p tcp --dport 21 -j ACCEPT

6) Not very funny but check once your username, password & host name carefully. :-)

Lock & Unlock a User Account in Linux

To Lock a user account 

$ sudo passwd -l username

To UnLock a user account

$ sudo passwd -u username

Root can log into locked account using su - username but can't log in using ssh.
Other users can't log into locked account using su - username as well as ssh.

The message is displayed when users try to access the locked account.

su: Authentication failure

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.