scrapy定时执行抓取任务

在ubuntu环境下，使用scrapy定时执行抓取任务，由于scrapy本身没有提供定时执行的功能，所以采用了crontab的方式进行定时执行：

首先编写要执行的命令脚本cron.sh

#! /bin/sh                                                                                                                                            

export PATH=$PATH:/usr/local/bin

cd /home/zhangchao/CVS/testCron

nohup scrapy crawl example >> example.log 2>&1 &

执行，crontab -e，规定crontab要执行的命令和要执行的时间频率，这里我需要每一分钟就执行scrapy crawl example这条爬取命令：

# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h  dom mon dow   command

*/1 * * * *  sh /home/zhangchao/CVS/testCron/cron.sh

编辑好了后，发现ubuntu的/var/log/下面没有crontab的日志，原因是因为ubuntu默认没有开启crontab的日志功能，执行如下操作：

emacs /etc/rsyslog.d/50-default.conf ，将cron.*这一行前的注释打开：

然后重启sudo  service rsyslog  restart

最后就可以使用tail –f  /var/log/cron.log查看crontab的日志了，可以看到cron.sh每一分钟被执行了一次：

借此机会复习下，crontab的常见格式：

每分钟执行  */1 * * * *

每小时执行     0 * * * *

每天执行        0 0 * * *

每周执行       0 0 * * 0

每月执行        0 0 1 * *

每年执行       0 0 1 1 *