/etc/passwd

/etc/passwd stores local account records in a colon-separated text format. It maps login names to numeric UIDs and records a primary GID, descriptive field, home path, and login program.

This is not necessarily every account known to the system. The Name Service Switch (NSS) can resolve accounts from files, directory services, system databases, or other configured sources. Use getent to query the resolved passwd database:

$ getent passwd
$ getent passwd root

The first command can disclose account names and metadata, so review output before sharing it publicly.

The seven colon-separated fields are:

1. Login name: The human-readable account name, such as root.
2. Password field: Usually x on a shadow-password system, indicating protected password data is stored separately.
3. UID: The numeric user identity. UID 0 has traditional superuser treatment.
4. Primary GID: The numeric ID of the account's primary group.
5. GECOS/comment: Descriptive account information, often internally comma-separated.
6. Home directory: The path used as the account's home setting; it may be absent on disk.
7. Login shell/program: The program requested for applicable login sessions, such as /bin/bash or a non-login program.

The kernel does not require UID values to be unique across malformed or deliberately duplicated records, but accounts that share a UID are indistinguishable for many ownership and permission decisions. Administrators should normally keep account UIDs unique.

That does not prove the account cannot authenticate by every method. SSH keys, certificates, tokens, or service-specific mechanisms may be independent. Likewise, an empty password field has security-sensitive behavior that depends on the authentication stack; do not create or “fix” it manually.

Do not infer account purpose from UID range alone without checking the distribution's policy. Allocation ranges vary, and centrally managed accounts may follow different conventions.

If a local passwd database truly requires manual repair, use vipw rather than an ordinary editor. It applies locking intended to avoid concurrent edits. Validate databases with tools such as pwck and maintain a recovery session before changing authentication files remotely.

To practice user and group records in a controlled environment, try these hands-on labs:

1. Manage Linux User Accounts with useradd, usermod, and userdel - Practice the complete lifecycle of user administration, from creating and securing new accounts to modifying and deleting them.
2. Manage Linux Groups with groupadd, usermod, and groupdel - Gain hands-on experience with core command-line utilities for group administration, including creating new groups and modifying user memberships.