Sintassi Cron
Posizioni dei campi, caratteri speciali, pianificazioni comuni e scorciatoie predefinite
Field Positions
| Field | Allowed Values | Special Chars | Example | Description |
|---|---|---|---|---|
Minute
|
0 - 59 |
* , - / |
30 | Minute of the hour (0=on the hour, 30=half past) |
Hour
|
0 - 23 |
* , - / |
14 | Hour of the day in 24-hour format (0=midnight, 14=2pm) |
Day of Month
|
1 - 31 |
* , - / ? L W |
15 | Day of the month; not all months have 31 days |
Month
|
1 - 12 or JAN-DEC |
* , - / |
6 | Month; names (JAN-DEC) are supported in most cron implementations |
Day of Week
|
0 - 7 or SUN-SAT |
* , - / ? L # |
1 | 0 and 7 both represent Sunday; 1=Monday ... 6=Saturday |
Special Characters
| Field | Allowed Values | Special Chars | Example | Description |
|---|---|---|---|---|
*
|
Any value |
* * * * * |
every | Match any value in this field — wildcard for all values |
,
|
Value list |
1,15 * * * * |
list | Specify multiple values; runs at minute 1 AND minute 15 |
-
|
Range |
9-17 * * * * |
range | Define range; 9-17 in hour field means every hour from 9am to 5pm |
/
|
Step value |
*/5 * * * * |
step | Step through range; */5 in minute field means every 5 minutes |
?
|
No specific value |
0 12 ? * MON |
ignore | Used in day-of-month or day-of-week to say 'don't care' (Quartz/Spring) |
L
|
Last |
0 0 L * * |
last | Last day of month or last weekday; L in day-of-week = Saturday (Quartz) |
W
|
Nearest weekday |
0 9 15W * * |
weekday | Nearest weekday to given day of month (Quartz/Spring only) |
#
|
Nth weekday |
0 10 * * 2#1 |
nth | Nth occurrence of weekday in month; 2#1 = first Tuesday (Quartz) |
Common Examples
| Field | Allowed Values | Special Chars | Example | Description |
|---|---|---|---|---|
* * * * *
|
Every minute |
* * * * * /path/to/cmd |
60x/hr | Run command every minute — most frequent standard cron interval |
0 * * * *
|
Every hour |
0 * * * * /path/cmd |
24x/day | Run at minute 0 of every hour (top of the hour) |
0 0 * * *
|
Daily at midnight |
0 0 * * * /backup.sh |
1x/day | Run once per day at midnight (00:00) |
0 9 * * 1-5
|
Weekdays 9am |
0 9 * * 1-5 /cmd |
Mon-Fri | Run at 9am Monday through Friday only |
0 0 * * 0
|
Weekly Sunday |
0 0 * * 0 /weekly.sh |
1x/week | Run at midnight every Sunday |
0 0 1 * *
|
Monthly |
0 0 1 * * /monthly.sh |
1st of month | Run at midnight on the 1st day of each month |
0 0 1 1 *
|
Yearly |
0 0 1 1 * /yearly.sh |
Jan 1st | Run at midnight on January 1st each year |
*/5 * * * *
|
Every 5 minutes |
*/5 * * * * /poll.sh |
12x/hr | Run every 5 minutes using step value |
*/15 9-17 * * 1-5
|
Every 15 min business hrs |
*/15 9-17 * * 1-5 /cmd |
business hrs | Every 15 minutes between 9am-5pm, weekdays |
0 2 * * *
|
Daily at 2am |
0 2 * * * /backup.sh |
2:00 AM | Common time for maintenance tasks — low traffic period |
30 23 * * 5
|
Friday 11:30pm |
30 23 * * 5 /cmd |
weekly | Specific day and time each week |
0 */6 * * *
|
Every 6 hours |
0 */6 * * * /sync.sh |
4x/day | Run at 00:00, 06:00, 12:00, and 18:00 each day |
Predefined Shortcuts
| Field | Allowed Values | Special Chars | Example | Description |
|---|---|---|---|---|
@yearly
|
0 0 1 1 * |
@yearly /cmd |
Jan 1 00:00 | Run once per year; same as @annually |
@annually
|
0 0 1 1 * |
@annually /cmd |
Jan 1 00:00 | Alias for @yearly |
@monthly
|
0 0 1 * * |
@monthly /cmd |
1st 00:00 | Run once per month at midnight on first day |
@weekly
|
0 0 * * 0 |
@weekly /cmd |
Sun 00:00 | Run once per week at midnight on Sunday |
@daily
|
0 0 * * * |
@daily /cmd |
00:00 | Run once per day at midnight; same as @midnight |
@midnight
|
0 0 * * * |
@midnight /cmd |
00:00 | Alias for @daily |
@hourly
|
0 * * * * |
@hourly /cmd |
top of hour | Run once per hour at the beginning of each hour |
@reboot
|
(on startup) |
@reboot /start.sh |
on boot | Run once at system startup; not supported in all cron implementations |
Domande Frequenti
Un'espressione cron standard ha 5 campi separati da spazi: minuto (0-59), ora (0-23), giorno del mese (1-31), mese (1-12), giorno della settimana (0-7). Si legge da sinistra a destra: '30 14 * * 1' significa 'alle 14:30 in qualsiasi giorno di qualsiasi mese, ma solo il lunedì'. L'asterisco * significa 'qualsiasi valore', quindi '* * * * *' viene eseguito ogni minuto.
cron è il daemon (servizio in background) che legge ed esegue i lavori pianificati. crontab (tabella cron) è il file che memorizza il programma, e anche il comando per modificarlo. Usa crontab -e per modificare i tuoi cron job, crontab -l per elencarli, e crontab -r per rimuoverli tutti. Ogni utente ha il proprio file crontab.
Cause comuni: (1) Problema di PATH — cron viene eseguito con PATH minimo; usa percorsi completi come /usr/bin/php. (2) Permessi — lo script deve essere eseguibile (chmod +x). (3) Nessuna nuova riga alla fine del file crontab. (4) Output a /dev/null che nasconde gli errori — reindirizza temporaneamente stderr: * * * * * /cmd >> /tmp/cron.log 2>&1. (5) Variabili d'ambiente non impostate.