A delay task
System delay task is a system task or tasks set only made after a certain time at a specified time, this command initiates tasks are disposable. General command is initiated delayed tasksat
1, the basic usage
| the specific time at + | Perform tasks in a specific time delay |
|---|---|
| at now + time | Delay the implementation of tasks from now after how long |
| at -l | View delay task |
| at -c job号 | View job details |
| at -r job号 | Cancel mission |
2, black and white list system delayed tasks
The user is present in the system can perform the task delayed
the establishment of the user delay the task blacklist, blacklist is /etc/at.deny, write user wang in the list of
results show that a user wang can not perform the task delayed
the establishment of the task delayed the user's whitelist , whitelist /etc/at.allow, by default, this list does not exist, once this list exists, only the root user and the user can perform on the white list of delayed tasks. When the presence of the white list, black list are disabled by default.
Written in the whitelist wang user, the user again switched showed wang user can perform tasks delay, the user can not dan
3, system delays the output of tasks
When the delay has the task to the task output is sent to the message originator's mailbox form
Second, regular tasks
Delay task at a one-time, only once, a permanent task is stored on disk, will never die.
Set the command mode Mode 1 ----
Tools developed for regular tasks: crontab
name of the service is: crontab.service
| crontab -e | edit |
|---|---|
| crontab -u | Specifies the user |
When developed using crontab scheduled tasks, time format is shown below
| field | allow values |
|---|---|
| minute | 0-59 |
| hour | 0-23 |
| day of month | 1-31 |
| month | 1-12(or names) |
| day of week | 0-7(0 or 7 is Sunday, or use name) |
As shown below, the first row indicates: Empty per minute / mnt
second line indicates: every / mnt 5 minutes emptied
third row indicates: every / mnt emptied under five minutes between 8:00 to 11:00
of line represents: 1 month and between 8 and 11 every 15 dot / mnt under five minutes emptied
fifth row indicates: 1 and 8 to No. 15 of June 11 to October every inter / mnt emptied under five minutes
sixth line represents: between every June to October 1, and 8:00 to 11:00 every Saturday and 15 6 to 10 months under five minutes empty / mnt
| crontab -l -u root | View all crontab under the root user |
|---|---|
| crontab -r -u root | All will delete all under the root user crontab |
Setting 2 ---- Profiles way
Go to the directory where the configuration file cd /etc/cron.d, write the file format exist view directory and write in this directory regular tasks we need to
view the files in a directory format sysstat
timing of writing tasks in the file wang
crontab set blacklist
Set blacklist user wang in the file /etc/cron.deny
crontab whitelist setting
Delay and whitelist similar tasks, timer task /etc/cron.allow whitelist, the user writes in wang list. By default, this list does not exist, once this list exists, only the root user and the user can perform on the white list of delayed tasks. When the presence of the white list, black list are disabled by default.
