Search notes:

/etc/passwd

User account information: each line represents a user and is colon-separated with the following fields:

username
password	nowadays usually `x`, see `/etc/shadow`
user id
default group id	See `/etc/group`
gecos
The user's home directory
The shell	The name of the program to be run when a user logs in, usually a shell.

In order to prohibit a user from logging in, the programm to be launched (7) might be set to /bin/false

The file should be edited with vipw.

See also