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This article introduces the knowledge of "what are the symbols commonly used in linux cron planning tasks". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

[root@wx-a] # crontab-- help

Crontab: invalid option -'-'

Crontab: usage error: unrecognized option

Usage: crontab [- u user] file

Crontab [- u user] [- e |-l |-r]

(default operation is replace, per 1003.2)

-e (edit user's crontab) Editing crontab work

-l (list user's crontab) to view the work of crontab

-r (delete user's crontab) delete all crontab tasks

-I (prompt before deleting user's crontab)

-s (selinux context)

By default, any user who is not included in / etc/cron.deny can execute "crontab-e" to edit their own routine commands.

The meaning of the representative

Minute

Hour

Date

Month

Zhou

Numeric range

0-59

0-23

1-31

1-12

0-7

When the number of week is 0-7, it all means "Sunday".

Auxiliary character

Special character

Representative meaning

* (asterisk)

It means to accept it at any time.

, (comma)

Means to divide a period of time, if you want to perform 2:00 and 4: 00:00

0 2 ~ 4 * command

The time parameter has five columns, and the second column is 2Jing, which represents 2:00 and 4:00.

-(minus sign)

Represents a range of time, such as every 10 minutes an hour between 7 and 10:00

Job: 10 7-10 * command

The second column becomes 7-10 for 7 8 9 10.

/ n (slash)

That n represents a number, which means an interval of n units, for example, every 5 minutes.

Then: * / 5 * command

It can also be written as 0-59 stroke 5 with the same meaning.

System task planning

[root@wx-a ~] # cat / etc/crontab

SHELL=/bin/bash

PATH=/sbin:/bin:/usr/sbin:/usr/bin

MAILTO=root

HOME=/

# For details see man 4 crontabs

# 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

Crontab-e is designed for the user's cron.

Basically, the minimum detection limit for the cron service is "minutes", so cron reads the data contents of / etc/crontab and / var/spool/cron every minute.

Standard output (stout): use > or > for code 1

Standard error output (stderr): code 2 uses 2 > or 2 >

Black hole / dev/null

Error output 2 > & 1

Cron allows scheduled tasks not to be output on screen using > / dev/null 2 > & 1

[root@wx-a ~] # crontab-l

* / 1 * echo "hello" > > / tmp/test.txt

[root@wx-a ~] # cat / tmp/test.txt

Hello

[root@wx-a ~] # cat / tmp/test.txt

Hello

Hello

Let the output go to the black hole.

[root@wx-a ~] # crontab-l

* / 1 * echo "hello"

[root@wx-a ~] # crontab-l

* / 1 * echo "hello" > / dev/null 2 > & 1 is output to the black hole.

For other help, check out man cron or man crontab.

Ps:ocsng linux client installation

Aptitude-y install gcc automake autoconf libtool make

Aptitude-y install dmidecode libxml-simple-perl libcompress-zlib-perl libnet-ip-perl libwww-perl libdigest-md5-perl libnet-ssleay-perl

Aptitude-y install libcrypt-ssleay-perl libnet-snmp-perl libproc-pid-file-perl libproc-daemon-perl net-tools libsys-syslog-perl pciutils smartmontools read-edid nmap

Tar-xvzf Ocsinventory-Agent-2.0.x.tar.gz

Cd Ocsinventory-Agent-2.0.x

Env PERL_AUTOINSTALL=1 perl Makefile.PL

Make

Make install

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