---
title: crontab — scheduled job management
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: How to create, check, and manage logs for scheduled jobs using crontab.
tags: program, Automation and scheduled tasks, crontab
---

**💬 "crontab command"**

crontab **executes tasks at scheduled times**. It is a basic tool for backups, cleanup, and batch jobs.

The most common issues are environment variables (PATH) and output redirection.

- **Concept**: Specifies the execution schedule in the order minute, hour, day, month, weekday.
- **Five fields**: the time is specified in this order: `* * * * *`.
- **Command**: write the command to run after the fields.
- **Output**: it is safe to append > logfile 2>&1.
## Commonly used options

| Option | Description |
| --- | --- |
| -l | View current schedules |
| -e | Edit schedules (uses editor) |
| -r | Delete all schedules (dangerous) |
| MAILTO= | Turns off or sets mail delivery |

## 3 essential command combinations

- `crontab -l` — view current schedules
- `0 3 * * * /opt/app/bin/backup.sh > /var/log/app/backup.log 2>&1` — backup every day at 03:00
- `*/5 * * * * /opt/app/bin/health.sh >/dev/null 2>&1` — health check every 5 minutes
**💬 "How should I use this when responding to incidents?"**

Common situations on production servers are organized below in order.

### Step 1 · View schedules

Check for duplicates with existing jobs.

```
crontab -l
```

### Step 2 · Add the job

Add it so that logs are kept.

```
crontab -e  # 0 3 * * * /opt/app/bin/backup.sh > /var/log/app/backup.log 2>&1
```

### Step 3 · Verify

Check the logs and execution history.

```
tail -n 20 /var/log/app/backup.log && grep CRON /var/log/syslog | tail -5
```

## How it is used in practice

### 1. Nightly backup

**Situation** — You need to back up a DB dump every day in the early morning.

```
0 3 * * * /usr/local/bin/db-dump.sh > /var/log/app/dump.log 2>&1
```

**Result** — The dump runs every day at 03:00 and logs are kept.

**Point** — Write scripts using absolute paths, and set PATH inside the script.

### 2. Temporary file cleanup

**Situation** — You need to periodically empty the cache directory.

```
30 4 * * * find /var/cache/app -type f -mtime +7 -delete > /dev/null 2>&1
```

**Result** — Cache files older than 7 days are cleaned up every day.

**Point** — For delete operations, narrow the target path and keep logs for verification.

## Important notes

- The cron environment differs from a login shell, so PATH and environment variables are empty. Use absolute paths.
- If you do not redirect output, mail can pile up or logs can be lost.
- crontab -r deletes all schedules. Back them up with -l before using it.
- If you do not check the server time zone, jobs may run at unexpected times.
## Actual execution screen

This is the result of checking the schedule list and backup execution log.

![crontab command execution result: schedule list and execution log](https://games.aidebatehub.com/assets/crontab-demo.png)

Production server in actual operation

---
Source (HTML): https://games.aidebatehub.com/programs/linux/automation/crontab.html
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