The original ser2net config used raw TCP accepters, but conman's
dev="host:port" speaks telnet protocol. This protocol mismatch caused
conman's telnet NVT state machine to strip bare CR characters from
device output — particularly from Dell switches that send \n\r (LF+CR)
line endings — producing stair-stepped and garbled terminal display.
Fix: change ser2net accepter from `tcp,IP,PORT` to
`telnet(rfc2217),tcp,IP,PORT`. With both sides speaking telnet, binary
mode is negotiated and CR/LF translation is handled correctly by the
telnet NVT layer. RFC2217 also enables baud rate negotiation for
future use.
Validated at the byte level: PTY capture confirms all prompts render
cleanly at column 0 with proper CRLF handling across 5+ Enter presses.
All 7 consoles connected, 7 log files actively capturing.
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Replace all occurrences of the fleet admin password with REDACTED_PASSWORD.
Git history will be rewritten next to purge it from all prior commits.
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The ser2net layer between conman and the serial devices was causing
stair-stepping in terminal output. conman's dev="host:port" uses telnet
protocol, but ser2net's accepter was raw TCP (no telnet mode). The telnet
NVT state machine in conman was stripping bare CR characters from device
output — particularly from Dell switches that use old-style \n\r (LF+CR)
line endings instead of standard \r\n. In telnet, a bare \r not followed
by \n or NUL is non-compliant and gets dropped, leaving bare \n that
causes stair-stepping in the raw-mode terminal.
Fix: conman now opens serial devices directly via the stable udev
symlinks (/dev/consoles/<name>) with seropts, eliminating the telnet
layer entirely. ser2net is stopped and disabled but remains installed
for emergency TCP access (documented workflow: stop conmand, start
ser2net, use telnet, then reverse).
Architecture change:
Before: device → serial → ser2net (raw TCP) → conman (telnet NVT) → terminal
After: device → serial → conman (direct) → terminal
Verified: 7/7 serial devices held by conmand, 7/7 log files capturing,
all \r bytes preserved in terminal output (confirmed via PTY capture).
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conmand was binding to localhost only (server loopback=on default), so
the conman client on workstations couldn't connect. The intended workflow
is: conman client (workstation) → conmand (pfv-tsys4:7890 over Tailscale)
→ ser2net (TCP 2001-2007) → serial device. Without remote conmand access,
users had to telnet directly to ser2net, which conflicts with conmand's
persistent connections (kickolduser kicks the telnet session immediately).
Changes:
- generate-config.sh: add server loopback=off to conman.conf so conmand
listens on 0.0.0.0:7890 (reachable via Tailscale)
- query-remote.sh: new script for workstations — installs conman client,
verifies connectivity, lists or connects to consoles
- README.md: clarify access model (conman primary, telnet emergency only
with conmand stopped). Document the kickolduser conflict.
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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.
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mrcharles