Crontab Scheduled Task configuration record, crontab task
First, preface
Today, simply record the configuration of the crontab
Ii. Catalogue of Crontab
/etc/crontab file This is the scheduled task for the system to run/var/spool/cron directory user-defined crontab tasks are placed in this directory ls–lrt/etc/cron* /etc/cron.deny Represents a user who cannot use the crontab command /etc/cron.allow represents a user who can use the crontab command by default, Cron.allow does not exist, if all exists, Cron.allow first
Third, crontab command syntax
Specific crontab--help or man crontab|morecrontab–l //View the current user's scheduled Tasks crontab–e //Edit the current user's scheduled Tasks Crontab–r// Delete the current user's scheduled tasks
Iv. crontab Task Format
* * * * /home/xxx/crontab/test.sh >/dev/null 2>&1 & Top 6 columns for the time being C1 ( 1-59) C2 ( 1-23,0 means midnight) C3 Day (1-31) C4 month (1-12) C5 Week (0-6,0 for Sunday, 1 for Monday, and so on) C6 the first 5 columns of the command to run indicate how often the command executes, the minimum frequency is once per minute, Where the value of CN can be expressed in four forms: * , */n , t1-t2, A,b,c when the C1 is *, the command is executed every minute when C1 is */n, the command is executed every n minutes when C1 is T1-t2, it represents from T1 Clock to T2 minutes time to execute the command when C1 is A,b,c, the a,b,c minute is executed to execute the command example call: * * * /home/xxx/crontab/test.sh >/dev/null 2>& Amp;1 represents a daily 12:12 execution script */2 * * * * /home/xxx/crontab/test.sh >/dev/null 2>&1 means every 2 minutes Execute a SCRIPT 0 * * 1-5 /home/xxx/crontab/test.sh >/dev/null 2>&1 The script is executed at 23 points every Monday to Friday 0 * * 0 mail-s "xxx "Xxx@mail.com </tmp/maildata means 19 points per Sunday to send mail to xxx@mail.com
V. Instructions on the Order
Explanation of/dev/null 2>&1 in the command 0 means that keyboard input 1 means that standard output 2 means Error Output 1. Create the test.sh, as follows #! /bin/bashecho "Time is" ' date ' 2. Adding timed Tasks * * * * * /home/xxx/crontab/test.sh >/home/xxx/crontab/test.log & The default is 1, and the following method is consistent * * * * * /home/xxx/crontab/test.sh 1>/home/xxx/crontab/test.log &* * * * * /home/xxx/crontab /test.sh >/home/xxx/crontab/test.log 2>&1 &3. Description 1 represents, standard output, so the above command will output the script output to the log file specified later, Instead of printing to the screen; 2 means, error output, &1 represents the description of the file, this indicates that the error message executed by the script is redirected to 1 (standard output) and 1 has been redirected to the specified log file, so the information will be output to the log file can not be written 2>1, missing & will be considered an error message output to the name 1 file
VI. matters of caution
1.shell environment variables to set the necessary environment variables crontab default does not include the environment for the current user of the system, so you need to add the necessary environment variables 2. Use the full path approach as much as possible and avoid using relative paths 3. Avoid repeated execution of the script if (EXEC ("PS -ef |grep ' php ' |grep ' updatescript ' |grep-v ' grep ' |wc-l ') > 2) {die (); } Grep-v ' grep ' indicates the result to filter out grep's line wc-l represents the number of rows that meet the criteria so you can tell if a script named Updatescript has been executed in the PHP process.
Vii. references
Http://www.cnblogs.com/kerrycode/p/3238346.htmlhttp://www.cnblogs.com/hazir/p/sudo_command.html
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