Perform Daily Operations at 9:45 PM | CronBase
45 21 * * * Every day at 9:45 PM
* In a Nutshell
The cron expression 45 21 * * * runs Every day at 9:45 PM. Running tasks daily at a consistent time, like 9:45 PM, is crucial for batch processing, nightly backups, or generating end-of-day reports. This schedule ensures data is processed in a predictable window, often after peak business hours, preventing performance impacts during the day and maintaining data currency.
* When to use this
Use 45 21 * * * when a recurring task needs to run Every day at 9:45 PM. This schedule is commonly associated with daily schedules and database backup and report generation workloads. It uses Standard (5-Field POSIX) syntax, supported by Unix cron daemons, cloud schedulers such as AWS EventBridge, and container orchestration platforms such as Kubernetes CronJob.
CronBase parses 45 21 * * * using a dialect-aware rules engine that identifies the Standard (5-Field POSIX) format, validates field structure against the Standard (5-Field POSIX) specification, and produces the translation above. Next run times are calculated by forward-scanning from the current UTC clock. Learn how CronBase works.
Platform Implementations
Bash
Prerequisites
Unix/Linux host with a cron daemon running (vixie-cron, cronie, or systemd-cron). The script at /usr/local/bin/run-task.sh must exist and be executable (chmod +x).
Configuration
Run crontab -e to open the crontab editor. Cron reads the server's local timezone; prefix with CRON_TZ=UTC before the expression to pin to UTC. Always redirect output with >> /var/log/cron-tasks.log 2>&1 to capture both stdout and stderr.
Gotchas
Cron jobs inherit a minimal PATH — use full binary paths or set PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin at the top of the crontab. For sub-hourly schedules, add flock -n /tmp/run-task.lock before the command to skip overlapping runs if the previous execution is still running.
# Add to crontab with: crontab -e
45 21 * * * /usr/local/bin/run-task.sh >> /var/log/cron-tasks.log 2>&1Last verified:
Nodejs
Prerequisites
Node.js 18+ with node-cron installed (npm install node-cron). Add "type": "module" to package.json to use the import syntax shown above.
Configuration
Pass { timezone: 'UTC' } as the third argument to cron.schedule(). Without this option the schedule uses the Node.js process timezone, which shifts during DST transitions when servers are not pinned to UTC.
Gotchas
node-cron uses standard 5-field cron syntax — not Quartz 6-field. If your job runs longer than the schedule interval the next trigger fires while the previous is still executing. Use a boolean guard or a queue to skip concurrent runs rather than relying on the scheduler to enforce it.
import cron from 'node-cron';
cron.schedule('45 21 * * *', async () => {
console.log('[cron] running at', new Date().toISOString());
// your task logic here
}, { timezone: 'UTC' });Last verified:
Python
Prerequisites
Python 3.8+ with apscheduler installed (pip install apscheduler). For Python 3.12+ use apscheduler>=3.10.
Configuration
CronTrigger.from_crontab() accepts a standard 5-field cron string. Always pass timezone='UTC' to both the BlockingScheduler constructor and the trigger to ensure consistent scheduling regardless of the server's locale.
Gotchas
BlockingScheduler.start() blocks the calling thread indefinitely. For a web application, use BackgroundScheduler instead and call scheduler.start() at application startup. APScheduler logs missed fires if the process is stopped and restarted — configure misfire_grace_time (in seconds) to control how late a missed job is allowed to run.
from apscheduler.schedulers.blocking import BlockingScheduler
from apscheduler.triggers.cron import CronTrigger
scheduler = BlockingScheduler(timezone='UTC')
@scheduler.scheduled_job(
CronTrigger.from_crontab('45 21 * * *', timezone='UTC')
)
def run_task() -> None:
print('task running')
# your task logic here
scheduler.start()Last verified:
Golang
Prerequisites
Go 1.18+ and github.com/robfig/cron/v3 (go get github.com/robfig/cron/v3).
Configuration
Always create the scheduler with cron.New(cron.WithLocation(time.UTC)). Without WithLocation, the library defaults to the server's local timezone. Call c.Start() to begin the scheduler, then block with select {} to keep the process alive.
Gotchas
robfig/cron v3 uses standard 5-field cron expressions by default. To add second-level precision (6 fields), pass cron.WithSeconds() to cron.New() — but this changes field positions, so never mix syntaxes in the same scheduler. Always check the error returned by c.AddFunc() — a malformed expression is silently ignored without it.
package main
import (
"fmt"
"time"
"github.com/robfig/cron/v3"
)
func main() {
c := cron.New(cron.WithLocation(time.UTC))
_, err := c.AddFunc("45 21 * * *", func() {
fmt.Println("task running at", time.Now().UTC())
// your task logic here
})
if err != nil {
panic(err)
}
c.Start()
defer c.Stop()
select {}
}Last verified:
Java
Prerequisites
Spring Boot 2.7+ (or Spring Framework 5.3+) with spring-context on the classpath. Annotate your @SpringBootApplication class with @EnableScheduling — without it, @Scheduled methods are silently ignored.
Configuration
Spring @Scheduled uses a 6-field Quartz-style expression: [sec] [min] [hr] [dom] [mon] [dow]. The expression 0 45 21 * * ? is derived from 45 21 * * * — a leading 0 is prepended for the seconds field, and ? replaces the unconstrained day field.
Gotchas
Standard Unix cron has 5 fields; Spring requires 6. Pasting a 5-field expression directly into @Scheduled shifts every field by one and the job misfires silently. Use ? for either dom or dow — Quartz does not allow both to be *.
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
@Component
public class ScheduledTask {
@Scheduled(cron = "0 45 21 * * ?")
public void runTask() {
System.out.println("task running at: " + java.time.Instant.now());
// your task logic here
}
}Last verified:
Kubernetes
Prerequisites
Kubernetes 1.21+ (CronJob API is GA). kubectl configured with cluster access. Container image must be pullable from within the cluster.
Configuration
Apply with kubectl apply -f cronjob.yaml. Check status with kubectl get cronjobs and inspect run history with kubectl get jobs. concurrencyPolicy: Allow is set because this schedule fires infrequently — parallel runs are acceptable.
Gotchas
Without startingDeadlineSeconds, a missed job (e.g., due to cluster downtime) triggers as soon as the controller recovers. Kubernetes 1.25+ supports timeZone: UTC in the spec to avoid timezone ambiguity. Keep successfulJobsHistoryLimit and failedJobsHistoryLimit low to avoid accumulating stale Job objects in the cluster.
apiVersion: batch/v1
kind: CronJob
metadata:
name: scheduled-task
spec:
schedule: "45 21 * * *"
concurrencyPolicy: Allow
jobTemplate:
spec:
template:
spec:
restartPolicy: OnFailure
containers:
- name: task
image: alpine:3.19
command: ["/bin/sh", "-c", "echo 'task running'"]Last verified:
AWS EventBridge Equivalent
Standard cron expressions often need conversion for AWS EventBridge schedules.
cron(45 21 * * ? *)Frequently Asked Questions
What specific task does the `45 21 * * *` cron schedule perform?
This cron schedule is configured to execute a specific task once every day, precisely at the 45th minute past the 21st hour. It triggers at the same time each night, ensuring consistent execution.
How does this schedule handle time zone changes or Daylight Saving Time (DST)?
Cron jobs operate based on the server's local time. When Daylight Saving Time begins or ends, the server's clock shifts, and the job will run according to the new local time. It's important to monitor your system during these transitions to ensure expected behavior.
How can I verify that the job scheduled for `45 21 * * *` is running correctly?
You can verify job execution by checking your system's logs for entries related to the task at the scheduled time. Additionally, monitoring the output or results of the job, such as generated files or database updates, provides concrete proof of successful runs.
What potential issues should I be aware of with a daily schedule?
A common consideration is the possibility of overlapping runs if a previous execution takes longer than 24 hours. Ensure your task is idempotent or implement locking mechanisms to prevent duplicate processing if a run is delayed and the next scheduled execution begins.
What is a common variation for a daily execution schedule?
A frequent variation involves adjusting the time slightly for less critical tasks, perhaps running every hour instead of precisely at the 45th minute past the 21st hour, to reduce resource contention or allow for more frequent, less impactful updates.
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