# Cis Ubuntu1804 V220 6 2 5

> Ensure no duplicate UIDs exist

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-6-2-5` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-6-2-5`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-6-2-5/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-ubuntu1804-v220-6-2-5

---


# 6.2.5 Ensure no duplicate UIDs exist (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

Although the `useradd` program will not let you create a duplicate User ID (UID), it is possible for an administrator to manually edit the `/etc/passwd` file and change the UID field.

## Rationale

Users must be assigned unique UIDs for accountability and to ensure appropriate access protections.

## Audit Procedure

### Command Line

Run the following script and verify no results are returned:

```bash
#!/usr/bin/env bash

{
  while read -r l_count l_uid; do
    if [ "$l_count" -gt 1 ]; then
      echo -e "Duplicate UID: \"$l_uid\" Users: \"$(awk -F: '($3 == n) { print $1 }' n=$l_uid /etc/passwd | xargs)\""
    fi
  done < <(cut -f3 -d":" /etc/passwd | sort -n | uniq -c)
}
```

## Expected Result

No output should be returned.

## Remediation

### Command Line

Based on the results of the audit script, establish unique UIDs and review all files owned by the shared UIDs to determine which UID they are supposed to belong to.

## References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

## CIS Controls

- v8: **5.2** Use Unique Passwords
- v7: **4.4** Use Unique Passwords