mrcharles
eb99b00a70
Solve the long-standing USB adapter enumeration shift problem: 9 Prolific
USB-to-DB9 adapters on pfv-tsys4 have no unique serial numbers and get
assigned /dev/ttyUSB0-8 based on enumeration order, which changes on every
reboot and breaks the old /root/conmap + manual screen workflow.
Solution: udev rules pin each adapter by its ID_PATH (physical USB port
topology), which is stable across reboots regardless of enumeration order.
Each adapter gets a named symlink in /dev/consoles/<name>. ser2net opens
these stable symlinks and exposes them on TCP ports (2001-2007) bound to
the Tailscale interface only. conman connects to those TCP ports for
session logging and multi-user console sharing.
Architecture (layered, no port sharing):
USB adapter → udev symlink → ser2net (TCP) → conman (logging + mux)
Port assignments (all on Tailscale IP 100.70.77.93):
2001 = pfv-core-sw01 2002 = pfv-tor3-mgmt 2003 = pfv-tor3-stor
2004 = pfv-rrinfra-rtr 2005 = pfv-r2-tor-top 2006 = subodev-torsw
2007 = pfv-r2-sw
Scripts (console/):
- mapping.txt: source of truth (TCP port | name | ID_PATH | baud | comment)
- generate-config.sh: generates udev rules, ser2net.yaml, conman.conf
entries from mapping.txt. Idempotent (markers in conman.conf for clean
regeneration). Uses | delimiter (ID_PATH values contain colons).
- setup.sh: full deploy — generate configs, create symlinks (udev trigger
+ manual fallback for already-discovered devices), create conmand
systemd unit (Debian doesn't ship one), restart services
- discover.sh: read-only USB adapter and service state discovery
- validate-conman.sh: verify conman→ser2net→device data path and log capture
Issues fixed during development:
- /dev/console is a kernel char device (major 5, minor 1) — cannot create
a directory there. Changed symlink namespace to /dev/consoles/.
- conman 0.3.x has no 'include' directive — CONSOLE entries written
directly into /etc/conman.conf between idempotent markers.
- Debian conman package has no systemd unit — created
/etc/systemd/system/conmand.service with After=ser2net ordering.
- conman.conf had no LOGDIR — logs weren't being written to
/var/log/conman/. Fixed by adding server logdir directive.
Validation: 7 symlinks resolving, 7 TCP ports on Tailscale, conmand with
7 consoles registered, 7 log files actively capturing console output,
both services enabled for reboot survival.
💘 Generated with Crush
Assisted-by: Crush:glm-5.2
4.1 KiB
Console Management (ser2net + conman)
Network-accessible serial console management for all production network switches and routers, running on pfv-tsys4 (storage server).
Architecture
USB-DB9 adapters → udev symlinks (/dev/consoles/<name>) → ser2net (TCP) → conman (logging + multiplexing)
ser2net owns the physical serial devices and exposes them on TCP ports
bound to the Tailscale interface only (100.70.77.93:200X). conman
connects to those TCP ports for session logging, output capture, and
multi-user console sharing.
conman and ser2net do NOT share ports — only one process can open a serial device at a time. ser2net owns the physical device; conman connects over TCP.
The USB Enumeration Problem (SOLVED)
The 9 Prolific USB-to-DB9 adapters (067b:2303) on pfv-tsys4 have no
unique USB serial numbers and get assigned /dev/ttyUSB0-8 based on
enumeration order, which shifts on every boot. This made the old
/root/conmap + manual screen workflow break after every reboot.
Fix: udev rules pin each adapter by its ID_PATH (physical USB port
topology), which is stable across reboots regardless of enumeration order.
Each adapter gets a named symlink in /dev/consoles/ that never changes.
The udev rules are generated from mapping.txt, which maps each adapter's
ID_PATH to a console name and TCP port. To re-map after physically moving
an adapter, update mapping.txt and re-run setup.sh.
Fallback: if udev trigger doesn't create symlinks for already-discovered
devices (common on first run), setup.sh creates them manually by matching
ID_PATH. On subsequent boots, udev creates them automatically.
Port Assignments
| TCP Port | Console Name | ID_PATH | Description |
|---|---|---|---|
| 2001 | pfv-core-sw01 | usb-0:1.5.4.4 | Dell PowerConnect 5448 (core switch) |
| 2002 | pfv-tor3-mgmt | usb-0:1.6.3.1 | Rack 3 management TOR switch |
| 2003 | pfv-tor3-stor | usb-0:1.6.3.3.2 | Rack 3 storage TOR switch |
| 2004 | pfv-rrinfra-rtr | usb-0:1.6.3.3.1 | Cisco router (rrinfra) |
| 2005 | pfv-r2-tor-top | usb-0:1.6.3.3.3 | Rack 2 top-of-rack switch |
| 2006 | subodev-torsw | usb-0:1.5.4.1 | Suborbital device TOR switch |
| 2007 | pfv-r2-sw | usb-0:1.6.3.2 | Rack 2 old Dell switch |
All ports listen on the Tailscale IP (100.70.77.93).
Scripts
| Script | Purpose |
|---|---|
mapping.txt |
Source of truth: TCP port ↔ ID_PATH ↔ name ↔ baud |
generate-config.sh |
Generates udev rules, ser2net.yaml, conman.conf from mapping.txt |
setup.sh |
Full deploy: generate configs, create symlinks, restart services |
discover.sh |
Read-only discovery of USB adapters, existing config, services |
Usage
Connect to a console
# Via conman (with logging + multiplexing):
conman -f pfv-core-sw01 # attach to console
conman -q # query status of all consoles
# Via telnet (direct, no logging):
telnet 100.70.77.93 2001 # pfv-core-sw01
# From any Tailscale-connected device:
telnet pfv-tsys4 2001
Re-deploy after changing mapping.txt
PROX_HOST=pfv-tsys4 bash tests/remote.sh prox 'bash /root/console/setup.sh'
Find the ID_PATH for a new adapter
PROX_HOST=pfv-tsys4 bash tests/remote.sh prox-file console/discover.sh
Then match the new adapter's ID_PATH to its physical location and add a line
to mapping.txt.
Files on pfv-tsys4
| File | Purpose |
|---|---|
/etc/udev/rules.d/99-console-ports.rules |
Stable symlinks by ID_PATH |
/etc/ser2net.yaml |
ser2net config (TCP ports → serial symlinks) |
/etc/conman.conf |
conman config (CONSOLE entries between markers) |
/etc/systemd/system/conmand.service |
systemd unit for conmand |
/root/console/mapping.txt |
Copy of the source-of-truth mapping |
/root/console/setup.sh |
Setup script (re-runnable) |
/root/console/generate-config.sh |
Config generator |
Old workflow (replaced)
The old /root/conmap file and manual screen sessions are no longer
needed. The new setup is fully automated and survives reboots.