It is possible to schedule the execution of tasks “on the fly”, without manually creating dedicated timer and service units by using systemd-run. In the example above the WantedBy keyword is used to establish a reverse (weak) dependency of a specific target unit ( timers.target – a target reached quite early in the boot process) on the timer unit we are configuring: before that target is reached, our unit should be activated. To make a timer be automatically activated at boot (or when another specific target is reached), all we have to do is to make sure it has an stanza, where we specify when the activation should happen. With all files in place, we run: $ sudo systemctl start. All we have to do is to place it, together with the service is should trigger, inside the /etc/systemd/system directory. Activating a timerĪctivating a timer is quite simple. To reference a service unit explicitly, we must use the Unit keyword. This can be useful, for example, to execute schedules missed due to a system powered down, the next time the machine is powered on.īy taking a closer look at the timer definition, we can notice that the service to be triggered is not explicitly mentioned: when this happens, Systemd looks for a service unit with the same name of the timer (so in this case rvice). If for whatever reason a scheduled run is missed, the next time the timer unit is activated, the service is launched immediately, if in the elapsed time it would have been triggered at least once. The other keyword, Persistent, takes a boolean value: if set to true, the last time the service was triggered by the timer is saved to disk. The default value for AccuracySec is 1 minute the best accuracy is obtained with the 1ns notation (1 nanosecond). In this case the value is 12h, so the command could be delayed for a maximum of 12 hours. The former is used to establish a maximum delay in which the service can be launched.
We can also observe two other keywords are used: AccuracySec and Persistent. The OnCalendar keyword is used to set a daily realtime schedule. This stanza is specific to timer units: it is where the schedule is defined. The section which interests us the most, however, is. Here it is used to provide a description of the unit: we can see that the timer is used to perform a “daily regeneration of man-db”. The first thing we can notice is the stanza, which is common to all the systemd unit types. To inspect the unit, we can use systemctl and the cat subcommand: $ systemctl cat man-db.timer The service unit activated by the timer ( ACTIVATES).The timer unit in which the schedule is set ( UNIT).How much times has passed since the last time the timer ran ( PASSED).How many times before the next time timer will run again ( LEFT).The next time the timer will run ( NEXT).It includes 6 columns, which describes, in order: Mon 00:00:00 CET 9h left Sun 00:00:16 CET 14h ago shadow.timer rvice Mon 00:00:00 CET 9h left Sun 00:00:16 CET 14h ago man-db.timer rvice Sun 19:36:06 CET 5h 15min left Sat 10:38:59 CET 1 day 3h ago systemd-tmpfiles-clean.timer rvice Here is an example of the output produced by the command: $ systemctl list-timers Unless the -all option is passed to the command, only the active timers are included in the result. To list all the active timer units in our system, we can launch the list-timers subcommand of systemctl. More examples can be found consulting the systemd.time manpage. We can provide a list of time values using the, character and specify a range of values using. The weekdays, if specified, must be in English, either in the abbreviated (Wed) or complete form (Wednesday) (the case doesn’t matter). The task will be executed the first day of each month at 00:00:00 The task will be executed every Monday at 00:00:00
The task will be executed each day at 00:00:00 The task will be executed at the beginning of each hour The task will be executed every two hours starting from 3:00 pm The task will be executed every two minutes starting from the minute 0 The task will be executed at 11:12:13 of the first and the fifth day of each month of the year 2020, but only if the day is a Thursday or a Friday The task will be executed on the 27th of May of the year 2020 at 00:00:00 The task will be executed the 27th of May of each year, but only on days from Monday to Wednesday
The task will be executed each Wednesday at 18:00
0 kommentar(er)
