nixos-servers/docs/user-management.md

User Management with Kanidm

Central authentication for the homelab using Kanidm.

Overview

• Server: kanidm01.home.2rjus.net (auth.home.2rjus.net)
• WebUI: https://auth.home.2rjus.net
• LDAPS: port 636

CLI Setup

The kanidm CLI is available in the devshell:

nix develop

# Login as idm_admin
kanidm login --name idm_admin --url https://auth.home.2rjus.net

User Management

POSIX users are managed imperatively via the kanidm CLI. This allows setting all attributes (including UNIX password) in one workflow.

Creating a POSIX User

# Create the person
kanidm person create <username> "<Display Name>"

# Add to groups
kanidm group add-members ssh-users <username>

# Enable POSIX (UID is auto-assigned)
kanidm person posix set <username>

# Set UNIX password (required for SSH login, min 10 characters)
kanidm person posix set-password <username>

# Optionally set login shell
kanidm person posix set <username> --shell /bin/zsh

Example: Full User Creation

kanidm person create testuser "Test User"
kanidm group add-members ssh-users testuser
kanidm person posix set testuser
kanidm person posix set-password testuser
kanidm person get testuser

After creation, verify on a client host:

getent passwd testuser
ssh testuser@testvm01.home.2rjus.net

Viewing User Details

kanidm person get <username>

Removing a User

kanidm person delete <username>

Group Management

Groups for POSIX access are also managed via CLI.

Creating a POSIX Group

# Create the group
kanidm group create <group-name>

# Enable POSIX with a specific GID
kanidm group posix set <group-name> --gidnumber <gid>

Adding Members

kanidm group add-members <group-name> <username>

Viewing Group Details

kanidm group get <group-name>
kanidm group list-members <group-name>

Example: Full Group Creation

kanidm group create testgroup
kanidm group posix set testgroup --gidnumber 68010
kanidm group add-members testgroup testuser
kanidm group get testgroup

After creation, verify on a client host:

getent group testgroup

Current Groups

Group	GID	Purpose
ssh-users	68000	SSH login access
admins	68001	Administrative access
users	68002	General users

UID/GID Allocation

Kanidm auto-assigns UIDs/GIDs from its configured range. For manually assigned GIDs:

Range	Purpose
65,536+	Users (auto-assigned)
68,000 - 68,999	Groups (manually assigned)

PAM/NSS Client Configuration

Enable central authentication on a host:

homelab.kanidm.enable = true;

This configures:

• services.kanidm.enablePam = true
• Client connection to auth.home.2rjus.net
• Login authorization for ssh-users group
• Short usernames (torjus instead of torjus@home.2rjus.net)
• Home directory symlinks (/home/torjus → UUID-based directory)

Enabled Hosts

• testvm01, testvm02, testvm03 (test tier)

Options

homelab.kanidm = {
  enable = true;
  server = "https://auth.home.2rjus.net";  # default
  allowedLoginGroups = [ "ssh-users" ];     # default
};

Home Directories

Home directories use UUID-based paths for stability (so renaming a user doesn't require moving their home directory). Symlinks provide convenient access:

/home/torjus -> /home/e4f4c56c-4aee-4c20-846f-90cb69807733

The symlinks are created by kanidm-unixd-tasks on first login.

Testing

Verify NSS Resolution

# Check user resolution
getent passwd <username>

# Check group resolution
getent group <group-name>

Test SSH Login

ssh <username>@<hostname>.home.2rjus.net

Troubleshooting

"PAM user mismatch" error

SSH fails with "fatal: PAM user mismatch" in logs. This happens when Kanidm returns usernames in SPN format (torjus@home.2rjus.net) but SSH expects short names (torjus).

Solution: Configure uid_attr_map = "name" in unixSettings (already set in our module).

Check current format:

getent passwd torjus
# Should show: torjus:x:65536:...
# NOT: torjus@home.2rjus.net:x:65536:...

User resolves but SSH fails immediately

The user's login group (e.g., ssh-users) likely doesn't have POSIX enabled:

# Check if group has POSIX
getent group ssh-users

# If empty, enable POSIX on the server
kanidm group posix set ssh-users --gidnumber 68000

User doesn't resolve via getent

1. Check kanidm-unixd service is running:

   systemctl status kanidm-unixd
   

2. Check unixd can reach server:

   kanidm-unix status
   # Should show: system: online, Kanidm: online
   

3. Check client can reach server:

   curl -s https://auth.home.2rjus.net/status
   

4. Check user has POSIX enabled on server:

   kanidm person get <username>
   

5. Restart nscd to clear stale cache:

   systemctl restart nscd
   

6. Invalidate kanidm cache:

   kanidm-unix cache-invalidate
   

Changes not taking effect after deployment

NixOS uses nsncd (a Rust reimplementation of nscd) for NSS caching. After deploying kanidm-unixd config changes, you may need to restart both services:

systemctl restart kanidm-unixd
systemctl restart nscd

Test PAM authentication directly

Use the kanidm-unix CLI to test PAM auth without SSH:

kanidm-unix auth-test --name <username>