Linux /etc/passwd File Formats | Linux etc passwd File Formats

In Unix-like Operating system the ' /etc/passwd ' file is a text-based database of information about users that may login to the system or other operating system user identities that own running processes.

The file's name originates from one of its initial functions as it contained the data used to verify password of user accounts. However, on modern Unix system the security-sensitive password information is instead often stored in a different file using shadow password, or other database implementations.

The ' /etc/passwd ' file typically has file system permissions that allow it to be readable by all users of the system (world-readable), although it may only be modified by the superuser or by using a few special purpose privileged commands.

File Format :-

The ' /etc/passwd ' file is a text file with one record per line. Each describing a user account. Each record consists of seven fields separated by colons ' : ' symbol.

Seven Fields Are:-

1. Username:

• The First field is username.
• It is used when a user log in.
• It should be between 1 to 32 characters in length. Case-sensitive, usually all lowercase.

2. Password:

• The second field stores information used to validate a user's password.
• An 'x' in the password field. It's mean the actual encrypted password information being stored in a separate shadow password ( '/etc/shadow' ) file.
• Setting this field to an asterisk  ( '*' )  is the typical way to deactivated an account to prevent it being used.

3. User Identifier ( UID ):

• The third field is the user identifier.
• The number that the operating system uses for internal purpose.
• It does not have to be unique.

• UID 0 (zero) is reserved for 'root'.
• UID 1-499 are researved for system users.
• UID above 500 are use for normal users.

4. Group Identifier ( GID ):

• The fourth field is the group identifier.
• The number identifies the primary group of the user. All files that are created by this user may initially be accessible to this group.
• Usually the group id will match the user id.

5. Gecos Field (General Electric Comprehensive Operating Supervisor / System ):

• The fifth field, called the Gecos field.
• It is commentary that describes the person or account.
• Typically, this is a set of comma-separated values including the user's full name and contact details.

6. Home Directory:

• The sixth field is the path t the user's home directory.
• The absolute path to the directory the user will be in when they log in. Usually '/home/username' ( eg,:- '/home/nish' ).
• All user's personal files, web pages, mail forwarding, etc. will be stored here.

7. Program or Shell:

• The seventh field is the program or Shell that is started every time the user logs into the system.
• For an interactive user, this is usually one of the system's command line interpreters (shells).
• Often set to '/bin/bash' to provide access to the bash shell.