Cowork: Session provisioning fails with 'useradd: cannot create directory /sessions'

Bug Report

Service: Cowork (Claude's online agent workspace)

Error:

RPC error: ensure user: useradd failed: exit status 12: user add: cannot create directory /sessions/amazing-youthful-hopper

Symptoms

• Every new Cowork session fails immediately after sending any message
• Error appears consistently across multiple attempts
• The Cowork service shows as "up" (HTTP responding) but session provisioning fails
• Multiple consecutive "Initial greeting and session start" tasks all fail with the same error

Root Cause (likely)

useradd exit code 12 indicates the server cannot create the user home directory under /sessions/. This is typically caused by:

• Full disk on the /sessions filesystem
• /sessions directory not mounted or mounted read-only
• Permission issue on the session provisioner

Impact

Cowork is completely unusable — no sessions can be started.

Reported by

User via Claude Code CLI on 2026-04-16.