What are the symbols commonly used in linux cron planning tasks
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[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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