ssh-doctor

A troubleshooting guide for SSH, the secure way to log in to another computer, on macOS. It focuses on Remote Login, the macOS SSH service, connections that close before sign-in, and stale sessions.

In plain words
What is it for?
Use it to check whether SSH works locally or remotely, inspect the SSH service and listening port, review configuration, and restart the service when needed.
Why use it?
It helps separate server, network, firewall, and configuration problems without exposing secrets or changing settings blindly.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/steipete/agent-scripts/ssh-doctor
Any agent
npx skills add steipete/agent-scripts --skill ssh-doctor
Clone the repo
git clone --depth 1 https://github.com/steipete/agent-scripts

Made for: Claude Code, Codex.

Per session 23 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,414 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00023 $0.01414
Opus 5 $0.00012 $0.00707
Sonnet 5 $0.00005 $0.00283
Haiku 4.5 $0.00002 $0.00141

Measured 2d ago against content hash b2f5918b9c88, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

ssh-doctor scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Asks for rootmediumPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

sudo systemsetup -getremotelogin
skills/ssh-doctor/SKILL.md · 147 lines

How it starts

The opening of the file, as written. The whole thing — 147 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SSH Doctor

Use when SSH connects then closes before auth, Remote Login seems advertised but unusable, or local/remote Mac SSH needs diagnosis.

Rules

  • Do not print secrets, tokens, full env, or broad secret grep output.
  • Validate locally first: loopback failure means server-side sshd/launchd/config; loopback success plus remote failure means network/firewall/filter/listen path.
  • Report suspicious config lines before changing /etc/ssh/sshd_config.
  • Prefer non-interactive SSH:
ssh -o RequestTTY=no -o RemoteCommand=none HOST 'hostname; id -un'

Baseline

hostname; id -un; sw_vers
ipconfig getifaddr en0
ipconfig getifaddr en1 2>/dev/null || true
ipconfig getifaddr en7 2>/dev/null || true
sudo systemsetup -getremotelogin
sudo systemsetup -setremotelogin on
sudo launchctl print system/com.openssh.sshd 2>&1 | head -80
sudo launchctl kickstart -k system/com.openssh.sshd
sudo lsof -nP -iTCP:22 -sTCP:LISTEN
nc -vz 127.0.0.1 22
ssh -4 -F /dev/null -o RequestTTY=no -o RemoteCommand=none [email protected] 'hostname; id -un'

Use BatchMode=yes only when password fallback would hang or prompt.

Config

sudo sshd -T 2>&1 | egrep -i '^(allowusers|denyusers|allowgroups|denygroups|listenaddress|maxstartups|logingracetime|usepam|passwordauthentication|pubkeyauthentication|authenticationmethods)'
sudo egrep -n '^[[:space:]]*(AllowUsers|DenyUsers|AllowGroups|DenyGroups|Match|MaxStartups|LoginGraceTime|ListenAddress|AuthenticationMethods|UsePAM|PasswordAuthentication|PubkeyAuthentication)\b' /etc/ssh/sshd_config /etc/ssh/sshd_config.d/* 2>/dev/null || true

Suspicious:

  • DenyUsers matching target user
  • restrictive AllowUsers / AllowGroups
  • Match block accidentally applying
  • tiny MaxStartups
  • tiny LoginGraceTime
  • ListenAddress missing target interface

Logs

sudo log show --last 30m --predicate 'process == "sshd" OR process == "launchd"' --style compact | tail -160

Important Mac symptom:

  • client: kex_exchange_identification: Connection closed by remote host
  • server log: Could not create new instance of inetd service: 67: Too many processes
  • launchctl print system/com.openssh.sshd: high copy count
  • many sshd-session: USER processes parented by PID 1

Read the full file on GitHub · 147 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 147 lines · 23 tokens per session scan B b2f5918b9c88

Subscribe to this mod's changes

ssh-doctor is a skill published in the GitHub repository steipete/agent-scripts (6,590 stars, last pushed today), licensed MIT. It adds 23 tokens to every session and 1,414 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it B with 1 finding (asks for root). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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