debug-cron-tmux-startup-failure

debug-cron-tmux-startup-failure is a skill for Claude Code, Codex from besoeasy/open-skills. It costs 95 tokens per session (1,841 once invoked), scanned A, original, MIT.

A troubleshooting workflow for services that should start after reboot through cron and tmux but silently stop. It focuses on shell differences at boot and logs written to temporary storage.

In plain words
What is it for?
Use it to diagnose missing tmux sessions, failed bots or daemons, empty boot logs, and @reboot jobs that appear to run but leave no process behind.
Why use it?
It explains why a command can work in an interactive terminal yet fail from cron, and why useful startup logs may disappear after reboot.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to diagnose missing tmux sessions, failed bots or daemons, empty boot logs, and @reboot jobs that appear to run but leave no process behind.

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Install with agentmods
npx agentmods add skills/besoeasy/open-skills/debug-cron-tmux-startup-failure
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.

Any agent
npx skills add besoeasy/open-skills --skill debug-cron-tmux-startup-failure
Clone the repo
git clone --depth 1 https://github.com/besoeasy/open-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for debug-cron-tmux-startup-failure

README.md
[![agentmods](https://agentmods.dev/badge/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure/github.svg)](https://agentmods.dev/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure)
Your own site
<a href="https://agentmods.dev/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure"><img src="https://agentmods.dev/badge/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure/github.svg" alt="Measured on agentmods" height="20"></a>

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Your own site · 80×15
<a href="https://agentmods.dev/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure"><img src="https://agentmods.dev/badge/skills/besoeasy/open-skills/debug-cron-tmux-startup-failure.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 95 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,841 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 2 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high YARA Match · line 76
    YARA rule matched a known malware signature (reverse shell, backdoor, ransomware, C2 framework, or info stealer).
    Fix: Remove the malware payload or compromised file entirely. Investigate how it entered the skill and audit all other artifacts for additional indicators of compromise.
  • medium Rogue Agent · line 19
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
How audits are shown
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 5.1 $0.00095 $0.01841
Opus 5 $0.00048 $0.00920
Sonnet 5 $0.00019 $0.00368
Haiku 4.5 $0.00010 $0.00184

Measured 7d ago against content hash aa7ab713db0f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

debug-cron-tmux-startup-failure scanned grade A with 0 findings 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 7d 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/debug-cron-tmux-startup-failure/SKILL.md · 129 lines

How it starts

The opening of the file, as written. The whole thing — 129 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debug Silent Cron+tmux Startup Failures

Diagnose why an @reboot cron job that is supposed to relaunch persistent tmux sessions (a bot, a dashboard, a watchdog) leaves nothing running, with no visible error and often no log file at all. The two classic silent killers are a bash-only source used inside tmux pane commands and boot-time logs written to a tmpfs /tmp.

Quick quality checklist

  • Reproduce under a cron-like environment (env -i ... SHELL=/bin/sh) so the pane shell matches cron's, not your interactive shell's
  • Confirm the pane shell before blaming the code: tmux panes run $SHELL (dash under cron), NOT the script's shebang
  • Treat missing boot logs in /tmp as expected on tmpfs systems; redirect boot logs to persistent storage
  • Confirm the final fix with a clean run in the exact cron environment, not just your shell

When to use

  • A service with an @reboot crontab entry is not running after reboot; crontab -l looks correct
  • The cron daemon log shows the job's CMD line fired, but the process is gone and there is no output file
  • tmux sessions are created by a start script but tmux ls reports no server running moments later
  • A watchdog or manager that auto-restarts via tmux also fails to bring the service back

Required tools / APIs

  • Linux with cron, tmux, and bash/dash (no external APIs)
  • Optional: systemd-tmpfiles-clean awareness for the /tmp boot-log gotcha

Steps

1. Establish that cron fired and what it ran

Check the cron daemon log for the @reboot job's start and end:

journalctl -b | grep -iE "cron.*dannyg|CMD|session opened|session closed"
# Expect roughly: CRON: (user) CMD (path/to/start.sh)  ...  then seconds later "session closed"

A session closed only a few seconds after CMD means the script ran to completion (or died fast). Next, look for the job's expected output and log files.

2. Check for output files and tmux state

ls -la /tmp/*.out /tmp/boot_*.log 2>/dev/null   # the redirect targets from the crontab/script
tmux ls                                          # "no server running" = server died
pgrep -af "your_service|tmux"

Read the full file on GitHub · 129 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. 7d ago First seen · 129 lines · 95 tokens per session scan A aa7ab713db0f

Subscribe to this mod's changes

debug-cron-tmux-startup-failure is a skill published in the GitHub repository besoeasy/open-skills (132 stars, last pushed 7d ago), licensed MIT. It adds 95 tokens to every session and 1,841 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-05.

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