Linux note 2-3 system delay and timing mechanism

3. System delay and timing mechanism **************

# # 1.at Delay # #
At time
At> Action
At> Ctrl+d
At> <EOT>
At-l Viewing wait tasks
ATRM Task Number Delete task

Example: Setting a delay task to create a new file in/mnt at 2:03 test

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When an action is executed with output
The output is sent to the task initiator as a message
Mail View message

Example: Writing script output hello.xx! Execute the script at 2:10 ticks

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As a result, the results do not appear on the interactive interface but are sent to the task performer by mail

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at Black and white list of users

/etc/at.deny blacklist, default exists
/etc/at.allow Whitelist, default does not exist, once there is a blacklist invalidation
And all ordinary users can perform at the power is forbidden only users in this file can perform at

example: On the Blacklist to test whether the student user can use the AT command by adding the student user

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add to the white list Add student user, test student user can use at command

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Once the whitelist is present, the blacklist expires

# 2. Recurring Tasks # #

Command mode initiated:

Crontab-u USERNAME-E
MM HH dd mm WW
MM/2 every two minutes
HH1-HH2 HH1 to Hh2 point in time
HH1,HH2 HH1 Point in time and Hh2 point in time
Crontab-l show tasks that are not in progress
Crontab-u username-r Delete all tasks for user

Example: New recurring task execute output "Hello" every Minute
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File mode initiated:
Vim/etc/cron.d/filename
MM HH dd mm WW username action
Or:
Echo ' MM hh DD MM WW username action ' >/etc/cron.d/filename

Example: initiating a task separately in the above two ways to create a new 5 file in/mnt

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Black and white list of cron users
/etc/cron.deny blacklist, default exists
/etc/cron.allow Whitelist, default does not exist, once there is a blacklist invalidation

And all ordinary users can execute Crontab's power is forbidden only users in this file can perform crontab
Note:

If a file is written to a user who does not perform the crontab permission, the user action can still be executed, because the user does not perform the crontab action, the action can still be executed

# 3. System temp File Management # #
Vim/usr/lib/tmpfiles.d/*.conf
Type filename Perm user group time

Example: D/mnt/westos 1777 root root 5
The shortest possible file created in this directory is 5s
Systemd-tmpfiles--create/usr/lib/tmpfiles.d/*
Systemd-tmpfiles--clean/usr/lib/tmpfiles.d/*

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Linux note 2-3 system delay and timing mechanism