What causes "unable to lookup user's group membership: %w" in hashicorp/nomad?

Run 'id ' on the host to reproduce the group lookup failure outside Nomad

unable to lookup user's group membership: %w

Error message

unable to lookup user's group membership: %w

What it means

getGroupsID calls user.GroupIds() to enumerate all groups the user belongs to; this error wraps any failure of that lookup. The validator cannot determine the user's group memberships, so HasValidIDs fails before it can check denied GIDs.

Source

Thrown at drivers/shared/validators/validators_unix.go:26

import (
	"fmt"
	"os/user"
	"strconv"
)

func getUserID(user *user.User) (UserID, error) {
	id, err := strconv.ParseUint(user.Uid, 10, 32)
	if err != nil {
		return 0, fmt.Errorf("unable to convert userid %s to integer", user.Uid)
	}

	return UserID(id), nil
}

func getGroupsID(user *user.User) ([]GroupID, error) {
	gidStrings, err := user.GroupIds()
	if err != nil {
		return []GroupID{}, fmt.Errorf("unable to lookup user's group membership: %w", err)
	}

	gids := make([]GroupID, len(gidStrings))

	for _, gidString := range gidStrings {
		u, err := strconv.ParseUint(gidString, 10, 32)
		if err != nil {
			return []GroupID{}, fmt.Errorf("unable to convert user's group %q to integer: %w", gidString, err)
		}

		gids = append(gids, GroupID(u))
	}

	return gids, nil
}

View on GitHub (pinned to 482b49bf1a)

Solutions

Run 'id <username>' on the host to reproduce the group lookup failure outside Nomad
Check /etc/nsswitch.conf group line and fix the misbehaving NSS module (sssd/ldap)
Verify the directory service (LDAP/AD) is reachable and responding
Restart sssd or clear its cache (sss_cache -E) if group enumeration is stuck

Defensive patterns

Strategy: retry

Validate before calling

cmd := exec.Command("id", username)
if err := cmd.Run(); err != nil {
	return fmt.Errorf("group lookup for %s currently fails on this host", username)
}

Try / catch

if err := validator.HasValidIDs(user); err != nil {
	var ctxErr error
	if errors.As(err, &ctxErr) && errors.Is(err, context.DeadlineExceeded) {
		// retry later; NSS/directory service may be transiently down
	}
	return err
}

Prevention

Keep /etc/nsswitch.conf group sources minimal and healthy
Monitor sssd/LDAP availability; cache group data where possible
Test 'id <task-user>' in host health checks
Avoid enormous supplemental group lists that can time out enumeration

When it happens

Trigger: Calling Validator.HasValidIDs(userName) when the underlying group membership lookup fails — typically the OS call getgrouplist / NSS group enumeration errors out for the given user.

Common situations: Broken NSS configuration (misconfigured sssd/ldap/nsswitch.conf), directory service timeouts or outages, extremely large group membership lists, or permissions issues reading group databases.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/2bac0f70cf590dbf. Report an issue: GitHub.