How to use the crontab command under Linux: sudo crontab-l

Cron is the next program in the Linux system that automatically executes a specified task.

The cron service is a built-in service for Linux, but it does not boot automatically. You can start and stop the service with the following command:

Linux Code

2. /sbin/service Crond Start
4. /sbin/service Crond Stop
6. /sbin/service Crond Restart
8. /sbin/service Crond Reload

The above 1-4 lines start, stop, restart the service, and reload the configuration, respectively.

To set cron to start automatically when booting, in the/etc/rc.d/rc.local script can be added /sbin/service crond start .

View, delete, modify

Cron saves the command line in the crontab (cron table) file, which is usually in the/etc directory. Each system user can have their own crontab (under/var/spool/cron/).

• File uses the contents of the file as a cron service configuration for a user, and the contents are copied to the Cron service's configuration file
• -U sets a user's cron service configuration, which is typically required by the root user when executing this command
• -l lists a user cron service configuration
• -R Delete a user's cron service configuration
• -e Edit a user's cron service configuration, when specified crontab does not exist, new, will use VI to open the configuration file for editing save after the exit, file syntax see after
• Crontab–v show The last edit time (available on some operating systems only)

Example: sudo crontab-lGrammareach line represents an instruction, which represents a scheduled task, each line consists of six parts separated by a space, the first 5 represents the time of the scheduled task execution, and the remainder is the command to be executed by the timed task, in the following format:

minute   Hour Sun Moon Week command
minute  hour  day  month  dayofweek  Command

• minute the first few minutes of each hour to perform the task, 0-59
• command specifies the program to execute

The first five items above can be used with the following four special symbols:

• * Indicates all values, such as the first bit using * indicates every minute
• /denotes each, as the first bit uses */5 to denote every 5 minutes
• -Represents a range of values, as the second bit uses 2-4 to indicate 2 to 4 points
• That represents a discrete number of values, such as the 2nd bit using 6,8 to represent 6 points and 8 points
• Specify "step": 8-14/2 for 8,10,12,14
• Specify a list: such as "1,2,3,4″," 0-4,8-12″

In the six fields of each row, except that the command is a field that must be specified each time, the other fields are optional fields, which can be determined visually. For a field that is not specified, "*" is used to fill its position.

Example: Execute the following command every 10 minutes

2.     5        *      *     *      ls     Specify the Daily  5 : Span class= "number" style= "Color:rgb (192,0,0)" >30   execute ls command   
4.     7        8        *     *     ls     Specify monthly 8 " 7 : 30 performs the ls command   
6.     5        8        6      *      ls     Specify annual 6 month 8 day 5 : 30 execute ls command   
8. 6 * * 0 ls specified per Sunday of 6: Execute ls command [note:0 means Sunday, 1 said the week 1, and so on, can also be expressed in English, Sun said Sunday, Mon said Monday and so on. ]

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How to use the crontab command under Linux: sudo crontab-l