System accounts
System accounts are special accounts used by the system and services rather than regular users.
Key Points
- UID Range: 1–499 (system accounts); root has UID 0.
- Purpose: Run system services (e.g.,
sshd,bind) and perform background tasks. - Login: Typically not used for interactive login.
- Shell Field: Non-login shells in
/etc/passwd(e.g.,/usr/sbin/nologin). - Home Directory: Often none or minimal, e.g.,
/var/run/sshd. - Password Field: Usually an asterisk
*in/etc/shadow.
Examples
| File | Example Entry | Description |
|---|---|---|
/etc/passwd |
sshd:x:103:65534::/var/run/sshd:/usr/sbin/nologin |
System account for SSH service; non-login shell |
/etc/shadow |
sshd:*:16874:0:99999:7::: |
No password; account cannot be used to log in |
Notes
- System accounts are essential for normal system operation.
- Do not delete system accounts unless certain it will not break functionality.
- Administrators must secure system accounts to maintain system security.