Detailed explanation and examples for this cron schedule pattern
0 */21 * * *0 0 */21 * * ?0 0 */21 * * ? *0 */21 * * *0 */21 * * * /path/to/commandcron: '0 */21 * * *'cron(0 \*/21 \* \* \*)0 */21 * * *"schedule": "0 */21 * * *"cron: '0 */21 * * *'schedule: "0 */21 * * *"placement: { constraints: [node.role == manager] }
labels: { cron: "0 */21 * * *" }CronScheduleBuilder.cronSchedule("0 */21 * * *")cron.schedule('0 */21 * * *', function() {
// Your code here
});from crontab import CronTab
cron = CronTab(user='username')
job = cron.new(command='/path/to/command')
job.setall('0 */21 * * *')# config/packages/messenger.yaml
framework:
messenger:
transports:
cron: '%env(MESSENGER_TRANSPORT_DSN)%'
options:
cron_expression: '0 */21 * * *'This cron expression is composed of 5 time/date fields:
| Field | Value | Description |
|---|---|---|
| Minute | 0 | 0 |
| Hour | */21 | Every 21 hours (0-23) |
| Day of Month | * | Every day of the month (1-31) |
| Month | * | Every month (1-12) |
| Day of Week | * | Every day of the week (0-6, where 0 is Sunday) |
In Quartz, we add a seconds field (and can replace * with ? in day-of-week):
| Field | Value | Description |
|---|---|---|
| Second | 0 | 0 |
| Minute | 0 | 0 |
| Hour | */21 | Every 21 hours (0-23) |
| Day of Month | * | Every day of the month (1-31) |
| Month | * | Every month (1-12) |
| Day of Week | ? | Any value (no specific value) |
AWS CloudWatch Events adds an optional year field:
| Field | Value | Description |
|---|---|---|
| Minute | 0 | 0 |
| Hour | */21 | Every 21 hours (0-23) |
| Day of Month | * | Every day of the month (1-31) |
| Month | * | Every month (1-12) |
| Day of Week | * | Every day of the week (0-6, where 0 is Sunday) |
| Year (Optional) | * | Every year |
Note that different systems interpret cron expressions slightly differently. The standard Unix format has 5 fields, while Quartz and AWS formats have additional fields. Some special characters like ?, L, W, and # are only supported in specific implementations.
This job runs every 21 hours
0 * * * *0 */2 * * *0 */3 * * *0 */4 * * *0 */6 * * *0 */8 * * *0 */12 * * *0 */5 * * *0 */7 * * *0 */9 * * *0 */10 * * *0 */11 * * *0 */13 * * *0 */14 * * *0 */15 * * *0 */16 * * *0 */17 * * *0 */18 * * *0 */19 * * *0 */20 * * *0 */22 * * *0 */23 * * *