# CIS Ubuntu 14.04 LTS - 6.2.16 Ensure no duplicate UIDs exist

> Verify no duplicate User IDs exist in /etc/passwd

- Skill: `cyberstrikeus/cis-ubuntu-14-04-lts-6-2-16-ensure-no-duplicate-uids-exist` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu-14-04-lts-6-2-16-ensure-no-duplicate-uids-exist`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu-14-04-lts-6-2-16-ensure-no-duplicate-uids-exist/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-ubuntu-14-04-lts-6-2-16-ensure-no-duplicate-uids-exist

---


# 6.2.16 Ensure no duplicate UIDs exist (Scored)

## Profile Applicability

- 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

Run the following script and verify no results are returned:

```bash
#!/bin/bash

cat /etc/passwd | cut -f3 -d":" | sort -n | uniq -c | while read x ; do
  [ -z "${x}" ] && break
  set - $x
  if [ $1 -gt 1 ]; then
    users=`awk -F: '($3 == n) { print $1 }' n=$2 /etc/passwd | xargs`
    echo "Duplicate UID ($2): ${users}"
  fi
done
```

## Expected Result

No output should be returned.

## Remediation

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.

## Default Value

Not applicable.

## References

None

## CIS Controls

16 Account Monitoring and Control - Account Monitoring and Control

## Profile

- Level 1