首先说说cron,它是一个linux下的定时执行工具。根用户以外的用户可以使用 crontab 工具来配置 cron 任务。所有用户定义的 crontab 都被保存在/var/spool/cron 目录中,并使用创建它们的用户身份来执行。要以某用户身份创建一个 crontab 项目,登录为该用户,然后键入 crontab -e 命令来编辑该用户的 crontab。该文件使用的格式和 /etc/crontab 相同。当对 crontab 所做的改变被保存后,该 crontab 文件就会根据该用户名被保存,并写入文件 /var/spool/cron/username 中。cron 守护进程每分钟都检查 /etc/crontab 文件、etc/cron.d/ 目录、以及 /var/spool/cron 目录中的改变。如果发现了改变,它们就会被载入内存。这样,当某个 crontab 文件改变后就不必重新启动守护进程了。
安装crontab:
yum install crontabs
说明:
/sbin/service crond start //启动服务
/sbin/service crond stop //关闭服务
/sbin/service crond restart //重启服务
/sbin/service crond reload //重新载入配置
查看crontab服务状态:service crond status
手动启动crontab服务:service crond start
查看crontab服务是否已设置为开机启动,执行命令:ntsysv
加入开机自动启动:
chkconfig –level 35 crond on
crontab命令:
功能说明:设置计时器。
语 法:crontab [-u ][配置文件] 或 crontab [-u ][-elr]
补充说明:cron是一个常驻服务,它提供计时器的功能,让用户在特定的时间得以执行预设的指令或程序。只要用户会编辑计时器的配置文件,就可以使 用计时器的功能。其配置文件格式如下:
Minute Hour Day Month DayOFWeek Command
参 数:
-e 编辑该用户的计时器设置。
-l 列出该用户的计时器设置。
-r 删除该用户的计时器设置。
-u 指定要设定计时器的用户名称。
crontab 格式:
基本格式 :
分钟 小时 日 月 星期 命令
* * * * * *
第1列表示分钟1~59 每分钟用*或者 */1表示
第2列表示小时1~23(0表示0点)
第3列表示日期1~31
第4列 表示月份1~12
第5列标识号星期0~6(0表示星期天)
第6列要运行的命令
记住几个特殊符号的含义:
“*”代表取值范围内的数字,
“/”代表”每”,
“-”代表从某个数字到某个数字,
“,”分开几个离散的数字
# Use the hash sign to prefix a comment
# +—————- minute (0 – 59)
# | +————- hour (0 – 23)
# | | +———- day of month (1 – 31)
# | | | +——- month (1 – 12)
# | | | | +—- day of week (0 – 7) (Sunday=0 or 7)
# | | | | |
# * * * * * command to be executed
crontab几个例子如下:
(1)第一个例子。
30 21 * * * /etc/init.d/nginx restart
每晚的21:30重启 nginx。
(2)第二个例子,也就是本教程测试的例子
* * * * * /usr/bin/php -f /root/test.php >> test.log
每一分钟执行/root/test.php文件,将结果输出到test.log中。
完成了上面基础工作后,就来看看怎么使用crontab定时执行PHP脚本:
(1)我在/root下新建test.php文件,内容如下:
复制代码 代码如下:
#!/usr/bin/php -q
echo date('Y-m-d H:i:s')."from http://www.phpddt.com \n";
?>
说明:你可以用whereis php查找php执行文件位置。
(2)然后crontab -e编写如下shell:
复制代码 代码如下:
* * * * * /usr/bin/php -f /root/test.php >> test.log
说明:test.php必须为可执行文件:chmod +x test.php
测试结果很正常,截图如下:
当然你可以用使用crontab -e继续添加任务,在/var/spool/cron下你可以看到一个root文件。
windows下直接用windows计划任务,通过bat打开网页就可以了。不像linux这么复制。

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SessionID is a mechanism used in web applications to track user session status. 1. It is a randomly generated string used to maintain user's identity information during multiple interactions between the user and the server. 2. The server generates and sends it to the client through cookies or URL parameters to help identify and associate these requests in multiple requests of the user. 3. Generation usually uses random algorithms to ensure uniqueness and unpredictability. 4. In actual development, in-memory databases such as Redis can be used to store session data to improve performance and security.

Managing sessions in stateless environments such as APIs can be achieved by using JWT or cookies. 1. JWT is suitable for statelessness and scalability, but it is large in size when it comes to big data. 2.Cookies are more traditional and easy to implement, but they need to be configured with caution to ensure security.


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