Sintaks Cron
Kedudukan medan, aksara khas, jadual biasa dan pintasan yang telah ditentukan
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 |
Soalan Lazim
Ungkapan cron standard mempunyai 5 medan yang dipisahkan oleh ruang: minit (0-59), jam (0-23), hari bulan (1-31), bulan (1-12), hari minggu (0-7). Baca dari kiri ke kanan: '30 14 * * 1' bermaksud 'pada 14:30 pada mana-mana hari mana-mana bulan, tetapi hanya pada hari Isnin'. Asterisk * bermaksud 'sebarang nilai', jadi '* * * * *' dijalankan setiap minit.
cron ialah daemon (perkhidmatan latar belakang) yang membaca dan melaksanakan kerja yang dijadualkan. crontab (jadual cron) ialah fail yang menyimpan jadual, dan juga arahan yang digunakan untuk mengeditnya. Gunakan crontab -e untuk mengedit cron job anda, crontab -l untuk menyenaraikannya, dan crontab -r untuk mengalih keluar semua. Setiap pengguna mempunyai fail crontab sendiri.
Punca biasa: (1) Masalah PATH — cron berjalan dengan PATH minimum; gunakan laluan penuh seperti /usr/bin/php. (2) Kebenaran — skrip mesti boleh dilaksanakan (chmod +x). (3) Tiada baris baharu di hujung fail crontab. (4) Output ke /dev/null menyembunyikan ralat — alihkan stderr sementara: * * * * * /cmd >> /tmp/cron.log 2>&1. (5) Pemboleh ubah persekitaran tidak ditetapkan.