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Codex MCP login fails with EOF parsing .credentials.json

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Source: Troubleshooting reference

Symptom. HTTP MCP servers report Unknown authentication and login fails with failed to parse credentials file and EOF while parsing a value at line 1 column 0. The active $CODEX_HOME/.credentials.json is empty. A second login can separately report Address in use when the first still owns the configured OAuth callback port.

Root cause. An empty credential file is invalid JSON, so Codex cannot read the store to update it. Disk exhaustion can leave a credential write incomplete. On Blackwell, inspected September 23, 2026, the ext4 credential file’s modification time was September 16 at 04:58:24.871558 UTC; the Codex logs_2.sqlite database contained 24 No space left on device errors in the 04:58:20–04:58:30 UTC window. This strongly implicates a failed write during disk exhaustion; the logs do not identify the credential writer itself. Freeing space afterward does not repair the file. The Codex 0.154.0 credential writer calls set_len(0) before write_all, so a failed replacement write can leave an empty store. A healthcheck detects this damage; it cannot make upstream writes atomic.

Confirm. Check the active directory, capacity, and callback listener without printing credentials. On Linux:

Terminal window
runtime_dir="${CODEX_HOME:-$HOME/.codex}"
stat -c '%n bytes=%s modified=%y' "$runtime_dir/.credentials.json"
df -h "$runtime_dir"
df -i "$runtime_dir"
ss -ltnp 'sport = :45231' # Blackwell; use the configured port on other hosts
bash ~/dotfiles/install/codex.sh check

Fix. Resolve capacity exhaustion first. End an outstanding login in its original terminal before starting another. Preserve the damaged file privately; if it is confirmed empty, replace it atomically with a mode-0600 file containing {}. Do not overwrite a nonempty store or silently reset it during bootstrap. Reauthenticate each affected server and verify a read-only tool operation. A successful codex mcp list --json with not_logged_in confirms that parsing is repaired, not that authentication is restored. Legacy NFS credentials may contain stale rotating refresh tokens; their presence alone does not establish a safe recovery copy.

Keep active SQLite state host-local; SQLite WAL does not support network filesystems. Relocating the runtime does not fix a failed credential writer; protect runtime storage from build/cache exhaustion and retain private, consistent backups. See Codex runtime storage.