# Linux crontab ## Brief 无论是做开发还是做运维的程序猿，crontab命令是必须用到的命令。 \##目录介绍 * /var/spool/cron/ 目录下存放的是每个用户包括root的crontab任务，每个任务以创建者的名字命名。**J在这里面改成自己的用户名，就能看到已经设置的crontab作业。** > ``` > sudo cat /var/spool/cron/root > ``` * /etc/crontab 这个文件负责调度各种管理和维护任务。J就是一些配置而已。 > ``` > sudo cat /etc/crontab > > SHELL=/bin/bash > PATH=/sbin:/bin:/usr/sbin:/usr/bin > MAILTO=root > HOME=/ > > # For details see man 4 crontabs > > # Example of job definition: > # .---------------- minute (0 - 59) > # | .------------- hour (0 - 23) > # | | .---------- day of month (1 - 31) > # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... > # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat > # | | | | | > # * * * * * user-name command to be executed > ``` * /etc/cron.d/ 这个目录用来存放任何要执行的crontab文件或脚本。我们还可以把脚本放在/etc/cron.hourly、/etc/cron.daily、/etc/cron.weekly、/etc/cron.monthly目录中，让它每小时/天/星期、月执行一次。J就是不用设置启动时间，直接放在这些目录下，就能定时执行。 ### 流程介绍 #### 1.查看crontab定时任务 ``` crontab -l sudo crontab -u root -l #查看指定用户的crontab ``` #### 2.编辑定时任务【删除-添加-修改】 ``` crontab -e sudo crontab -u root -e #编辑指定用户的crontab ``` ``` 0 12 * * * (/usr/local/bin/python /data2/test2/data/GetDictData.py >/dev/null 2>&1 &) ``` * The & makes the command run in the background. * 在shell脚本中，默认情况下，总是有三个文件处于打开状态，标准输入(键盘输入)、标准输出（输出到屏幕）、标准错误（也是输出到屏幕），它们分别对应的**文件描述符**是0，1，2 。 * 1，对于下面两个命令其实效果一样。一般来说，"1>" 通常可以省略成 ">"。 * `ls GetDictData.py 1> test.out` * `ls GetDictData.py > test.out` * **就是说指定1和2可以分别输出正确和错误的结果**。**&2表示2输出通道，&1表示1输出通道。** * `ls a.txt b.txt 1>file.out 2>&1` * 输出`ls: b.txt: No such file or directory a.txt` * 输出不只1和2，还有其他的类型，这两种只是最常用和最基本的。 * 可以将/dev/null看作"黑洞"。它非常等价于一个只写文件. 所有写入它的内容都会永远丢失。而尝试从它那儿读取内容则什么也读不到。然而，/dev/null对命令行和脚本都非常的有用。 * 禁止标准输出。`cat $filename >/dev/null` # 文件内容丢失，而不会输出到标准输出。 * 禁止标准错误：`2>/dev/null`这样错误信息\[标准错误]就被丢到太平洋去了。 * `1>/dev/null` 首先表示标准输出重定向到空设备文件，也就是不输出任何信息到终端，说白了就是不显示任何信息。 `2>&1` 接着，标准错误输出重定向等同于 标准输出，因为之前标准输出已经重定向到了空设备文件，所以标准错误输出也重定向到空设备文件。 ### 实际例子 ```python #!/usr/bin/env python #coding=utf-8 import urllib import urllib2 import sys import os import time import datetime import socket import copy import logging import logging.handlers reload(sys) sys.setdefaultencoding('utf8') socket.setdefaulttimeout(2.0) __version = '1.1' __author = 'jimmylian' etcdir = '' datadir = '' logdir = '' def GetLogger(logdir, loglevel): """keep logfile change another file everyday""" filename = r"/log_update" myloglevel = 20 tmploglevel = int(loglevel) / 10 * 10 if tmploglevel >= 0 and tmploglevel <= 50: myloglevel = tmploglevel handler = logging.handlers.RotatingFileHandler(logdir+filename, maxBytes = 20*1024*1024, backupCount = 10) fmt = '%(asctime)s [line:%(lineno)d] [%(levelname)s] %(message)s' formatter = logging.Formatter(fmt) handler.setFormatter(formatter) logger = logging.getLogger('GetDictData') logger.addHandler(handler) logger.setLevel(myloglevel) return logger def GetDateBefore(daydelta,split=''): today = datetime.date.today() bfyesterday = today - datetime.timedelta(days = daydelta) if split != '': fmt = '%Y'+split+'%m'+split+'%d' else: fmt = '%Y%m%d' return bfyesterday.strftime(fmt) def DownHttpFile(url, filename, logger): tmpfile = "%s%s_tmp"%(datadir, filename) try: f = urllib2.urlopen(url) data = f.read() with open(tmpfile, 'wb') as code: code.write(data) except Exception, e: logger.error("download file error %s"%e) return False filepath = "%s%s"%(datadir, filename) os.rename(tmpfile, filepath) return True def process(logger): url = "http://XXXX.cn/XXX_info_1_%s"%(GetDateBefore(1, '')) flag = DownHttpFile(url, "info_1.txt", logger) path = '%sinfo_1.txt'%(datadir) destpath = '/info_1_%s.txt'%(GetDateBefore(1, '')) if not flag: if os.path.exists(destpath): os.unlink(destpath) logger.info("download file %s failed"%(url)) return os.rename(path, destpath) logger.info("download file %s done"%(url)) rmpath = '/info_1_%s.txt'%(GetDateBefore(3, '')) if os.path.exists(rmpath): os.remove(rmpath) logger.info("remove file %s done"%(rmpath)) else: logger.info("remove file %s failed"%(rmpath)) def process1(logger): url = "http://XXXX.cn/XXX_info_2_%s"%(GetDateBefore(1, '')) flag = DownHttpFile(url, "info_2.txt", logger) path = '%sinfo_2.txt'%(datadir) destpath = '/info_2_%s.txt'%(GetDateBefore(1, '')) if not flag: if os.path.exists(destpath): os.unlink(destpath) logger.info("download file %s failed"%(url)) return os.rename(path, destpath) logger.info("download file %s done"%(url)) rmpath = '/info_2_%s.txt'%(GetDateBefore(3, '')) if os.path.exists(rmpath): os.remove(rmpath) logger.info("remove file %s done"%(rmpath)) #os.system("/data1/XXXXX/upload/apache-cat-8.5.71/bin/shutdown.sh") #time.sleep(10) #os.system("/data1/XXXXX/upload/apache-cat-8.5.71/bin/startup.sh") #logger.info("restart tomcat success") else: logger.info("remove file %s failed"%(rmpath)) def __main__(): global datadir global logdir mybasedir = "%s"%(os.path.dirname(sys.argv[0])) if mybasedir == '': mybasedir = '.' datadir = "%s/data/"%(mybasedir) logdir = "%s/log/"%(mybasedir) logger = GetLogger(logdir, 20) runstr = '' for keys in sys.argv: runstr = "%s %s"%(runstr, keys) logger.info(runstr) process(logger) process1(logger) if __name__ == "__main__": __main__() ``` ## Reference * [Linux Crontab 定时任务](https://www.runoob.com/w3cnote/linux-crontab-tasks.html) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://jimmy-walker.gitbook.io/linux-shell/linux-brief/linux-crontab.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.