September 5, 2015 Course assignments (practice)

1. Summarize the detailed usage method of the task plan (at, crontab) on Linux system;

AT command:

To host a job that runs in the future time:

Support for using job queues:
The default is a queue;

Ctrl+d

At [option] ... Time

Time:
(1) Absolute time
HH:MM,
Mmdd[cc]yy, Mm/dd/[cc]yy, dd.mm.[cc]yy or [cc]yy-mm-dd
Tomorrow
(2) Relative time
now+ #UNIT
Minute, hour, day, week
(3) Blur time
Midnight
Noon
Teatime

Common options:
-Q queue:at Job queue;
-f/path/from/somefile: Reads the job to be run from the specified file;
-L: View a list of such running jobs in the job queue; equivalent to using the ATQ command;
-C At_job_num: Look at the contents of the running job;
-D: Delete the specified job; equivalent to ATRM

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Crontab: Recurring Task Schedule

Daemon: Crond

There are two types of recurring tasks:
(1) System cron task; There is no default running user identity, so you need to specify the additional runner;
/etc/crontab

Vim command

# Example of Job definition:
#.----------------Minute (0-59)
# | .-------------Hour (0-23)
# |  | .----------Day of Month (1-31)
# |  |  | .-------month (1-12) OR jan,feb,mar,apr ...
# |  |  |  | .----Day of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat
# |  |  |  | |
# * * * * * * user-name command to be executed

                     7 fields:    
                         Top 5 fields: Point in time    
                         User-name: Run tasks as a user    
                         command to being executed: To run the task            

(2) User Cron Task: Submitted by a user, the default is to run as the submitter, so there is no need to specify the additional runner;
/var/spool/cron/username

VIM command; not recommended
crontab Command: Recommended

# Example of Job definition:
#.----------------Minute (0-59)
# | .-------------Hour (0-23)
# |  | .----------Day of Month (1-31)
# |  |  | .-------month (1-12) OR jan,feb,mar,apr ...
# |  |  |  | .----Day of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat
# |  |  |  | |
# * * * * * command to be executed

                     5 time points:    
                         minutes: Valid range of values 0-59;    
                         hours: 0-23    
                         Day: 1-31    
                         Month: 1-12    
                         weeks: 0-7

Note: The date of the month and the number of weeks, not recommended to use at the same time;

For example:
6 * * * *

Time notation:

*: Each time point in the valid value range of the time point;
-: A specific continuous time range, 3-7
,: A discrete point in time, 3,5,7
/#: The amount of time in a valid time frame, for specifying the frequency;
1-30/4, */4

5 */3 * * */bin/echo "howdy"

5 7 * * 1-5/bin/echo "Howdy"

                     crontab command:    
                         crontab [-u user] [-l |- R | -e]    
                            -u User: Not managing your own cron task, but specifying the target user's cron task ; Root only has permissions to manage other users ' cron tasks; The default is to manage their own;

-l:list, list the tasks;
-r:remove to remove all tasks;
-e:edit, edit, open a default editor for the current shell session to edit the cron task table;

Attention:
(1) If you do not want to receive notification messages for task execution results:
COMMAND >/dev/null
COMMAND &>/dev/null
(2) for crontab file,% has a special function, if the command will appear in the%, remember to escape, or use single quotation marks to its reference;
(3) Crontab's path variable is not exactly the same as the user's variable, so it is recommended that the task in cron use an absolute path
/root/bin/a.sh

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Practice:

2, every Monday to Saturday 3:20 A.M., run the tar command to save the/etc/directory, storage location is/BACKUPS/ETC-YYYY-MM-DD;

[[email protected] ~]# mkdir/backups///Create Directory

[Email protected] ~]# Echo 3 * * 1-6/bin/tar-cvf/backups/ect-$ (date +%f). Tar "/etc >>/var/spool/cron/roo T

If: every Monday to Saturday 3:20 A.M., run the CP command to save the/etc/directory, storage location is/BACKUPS/ETC-YYYY-MM-DD;

[[email protected] ~]# echo "3 * * 1-6/bin/cp-a/etc/backups/ect-$ (date +%f)/" >>/var/spool/cron/root

3, every Sunday 2:30 A.M., run the tar command to backup the/etc/fstab file, the storage location is/BACKUP/FSTAB-YYYY-MM-DD-HH-MM-SS;

[Email protected] ~]# echo "2 * * 0/bin/tar-cvf/backups/fstab-$ (date +%f-%h-%m-%s). Tar"/etc/fstab >>/va R/spool/cron/root

4, every night 12 o'clock, get all the lines in the/proc/meminfo file starting with S or M, appended to the/statistics/meminfo.txt file, and the daily message before, to add a similar =============== separator line;

[Email protected] ~]# mkdir statistics

[Email protected] ~]# crontab–e

Save exit after editing the following content
0 0 * * * echo-e "====================\n" + ' egrep ' ^[sm] '/proc/meminfo ' >>/statistics/meminfo.txt

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September 5, 2015 Course assignments (practice)