cron

A guide to scheduling commands on Linux, macOS, and similar systems. It covers cron for recurring jobs, at for one-time jobs, and launchd for scheduled macOS tasks.

In plain words
What is it for?
Use it to write cron schedules, configure crontab entries, run a command once later, create macOS launchd files, or investigate scheduled-job failures.
Why use it?
It helps you run maintenance scripts and other commands automatically without remembering to start them yourself, and troubleshoot schedules that do not run.

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/bug-ops/zeph/cron
Any agent
npx skills add bug-ops/zeph --skill cron
Clone the repo
git clone --depth 1 https://github.com/bug-ops/zeph

Made for: Claude Code, Codex.

Per session 79 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,806 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 $0.00079 $0.03806
Opus 5 $0.00039 $0.01903
Sonnet 5 $0.00016 $0.00761
Haiku 4.5 $0.00008 $0.00381

Measured 2d ago against content hash 7be9f425ca0c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

cron 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 crontab -u username -e
.zeph/skills/cron/SKILL.md · 472 lines

How it starts

The opening of the file, as written. The whole thing — 472 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Task Scheduling with Cron, At, and Launchd

Cron Expression Format

┌─────────── minute (0-59)
│ ┌───────── hour (0-23)
│ │ ┌─────── day of month (1-31)
│ │ │ ┌───── month (1-12 or JAN-DEC)
│ │ │ │ ┌─── day of week (0-6, SUN-SAT; 7 = SUN on some systems)
│ │ │ │ │
* * * * * command

Special Characters

Character Meaning Example
* Any value * * * * * (every minute)
, List 1,15,30 (at 1, 15, 30)
- Range 1-5 (1 through 5)
/ Step */5 (every 5 units)

Common Expressions

Expression Schedule
* * * * * Every minute
*/5 * * * * Every 5 minutes
*/15 * * * * Every 15 minutes
0 * * * * Every hour (at :00)
0 */2 * * * Every 2 hours
30 * * * * Every hour at :30
0 0 * * * Daily at midnight
0 6 * * * Daily at 6:00 AM
0 8,12,18 * * * At 8 AM, noon, 6 PM
0 9-17 * * * Every hour from 9 AM to 5 PM
0 0 * * 0 Weekly on Sunday at midnight
0 0 * * 1-5 Weekdays at midnight
0 0 * * 6,0 Weekends at midnight
0 0 1 * * First day of every month
0 0 1 1 * Yearly on January 1
0 0 1 */3 * Every 3 months (quarterly)
0 0 15 * * 15th of every month
5 4 * * 0 Sunday at 4:05 AM
0 22 * * 1-5 Weekdays at 10 PM

Predefined Shortcuts

Shortcut Equivalent Description
@reboot Run once at startup
@yearly / @annually 0 0 1 1 * Once a year (Jan 1)
@monthly 0 0 1 * * Once a month (1st)
@weekly 0 0 * * 0 Once a week (Sunday)
@daily / @midnight 0 0 * * * Once a day
@hourly 0 * * * * Once an hour

Crontab Management

# Edit current user's crontab
crontab -e

# List current user's crontab
crontab -l

# Remove current user's crontab (careful!)
crontab -r

# Edit crontab for another user (requires root)
sudo crontab -u username -e

# List another user's crontab
sudo crontab -u username -l

# Create crontab from file
crontab mycrontab.txt

# Backup crontab
crontab -l > crontab-backup.txt

# Restore crontab from backup
crontab crontab-backup.txt

Read the full file on GitHub · 472 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 · 472 lines · 79 tokens per session scan B 7be9f425ca0c

Subscribe to this mod's changes

cron is a skill published in the GitHub repository bug-ops/zeph (57 stars, last pushed 8d ago), licensed MIT. It adds 79 tokens to every session and 3,806 once invoked, about $0.0004 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.