# Cis Ubuntu1804 V220 4 5 6

> Ensure nologin is not listed in /etc/shells

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-4-5-6` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-4-5-6`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-4-5-6/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- 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-v220-4-5-6

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# CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 4.5.6

## Profile Applicability

- Level 2 - Server
- Level 2 - Workstation

## Description

`/etc/shells` is a text file which contains the full pathnames of valid login shells. This file is consulted by `chsh` and available to be queried by other programs.

Be aware that there are programs which consult this file to find out if a user is a normal user; for example, FTP daemons traditionally disallow access to users with shells not included in this file.

## Rationale

A user can use `chsh` to change their configured shell.

If a user has a shell configured that isn't in in `/etc/shells`, then the system assumes that they're somehow restricted. In the case of `chsh` it means that the user cannot change that value.

Other programs might query that list and apply similar restrictions.

By putting `nologin` in `/etc/shells`, any user that has `nologin` as its shell is considered a full, unrestricted user. This is not the expected behavior for `nologin`.

## Audit Procedure

### Command Line

Run the following command to verify that `nologin` is not listed in the `/etc/shells` file:

```bash
grep '/nologin\b' /etc/shells
```

### Expected Result

Nothing should be returned.

## Remediation

### Command Line

Edit `/etc/shells` and remove any lines that include `nologin`.

## References

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

## CIS Controls

v8 - 3.3 Configure Data Access Control Lists - Configure data access control lists based on a user's need to know.

v7 - 14.6 Protect Information through Access Control Lists.

## Profile Applicability

- Level 2 - Server
- Level 2 - Workstation

## Assessment Status

Automated