CRONTAB :
The crontab command submits, edits, lists, or removes cron jobs.
This command is a command and script schedular.
It runs task scheduling daily,hourly,weekly,monthly, etc.
It also allow users to setup their own schedules.
Example : We uses this command for system auditing ; running backup scripts.
Service : crond
It runs
]# crontab -l -- Lists cron jobs for user himself.
]# crontab -lu proco -- Lists cron jobs for user proco (Only root can execute this command).
]# crontab -eu proco -- Edits user proco's cron file stored at "/var/spool/cron/proco".
]# crontab -ru proco -- Removes cron jobs for user himself.
Format :
MIN HOURS DAYOFMONTH MONTH WEEKDAY COMMAND
(0-59) (0-23) (1-31) (1-12) (0-6 0=SUN) /vz/backup/vzbackup.sh >/dev/null 2>&1
Eg. :
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
Here, we dump data using above "vzbackup.sh" script. Crontab will execute this script daily at 21'st hour of the day.
An * (asterisk), meaning all allowed values. To run a job every hour, specify an asterisk in the hour field.
To write the time to the console every hour on the hour, enter:
0 * * * * echo The hour is `date` . >/dev/console
IMP Files/Dir for crontab :
File:/etc/crontab -- This file contains few directories as below. Script placed in a specific directory will execute according.
File:/var/spool/cron/{root,prem,etc} -- This directory contains separate file for separate user. its a schedular file as below.
File:/etc/cron.deny -- Specifies a list of users denied access to the crontab command.
[root@tlv1 etc]# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly
---------------------------------------------------
[root@tlv1 ~]# cat /var/spool/cron/root
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
---------------------------------------------------
Example:
Please set this cron to run every day at 11.55pm.
http://experiencesilk.com/duniya_dekhegi/cron_winners.php
Ans:
[root@experiencesilk cron]# cat root
55 23 * * * /usr/bin/php -q /var/www/html/duniya_dekhegi/cron_winners.php
=======================================
at command :
The Linux “at” command used for scheduling jobs. But “at” command can set the job run only once. The “at” daemon can be used to run a command or script of your choice. From the command line, you can run the “at” time command to start a job to be run at a specified time. That time can be now; in a specified number of minutes, hours, or days; or at the time of your choice. Spool area for at command is /var/spool/at/ directory. For normal users, permission to use at command is determined by the file /etc/at.deny. The file /etc/at.deny is checked, every user name not mentioned in it is then allowed to use at.
SYNTAX :
]# at <time>
Here, time format can be :
now
midnight - (12:00AM)
noon - (12:00PM)
teatime - (4:00PM)
14:23 (24 hours format) OR 02:23PM (12 hours format)
now + 05/03/13 - Its MMDDYY format. Here date is 3rd May, 2013. (now = at same time)
now + 10 minutes
now + 2 hours
now + 1 day - After 24 hours.
now + 1 week - After 7 days.
3:00 05/03/13 - On specified date and time.
The Linux atq command lists the user’s pending jobs, unless the user is the superuser; in that case, everybody’s jobs are listed. The format of the output lines (one for each job) is: Job number, date, hour, job class.
The Linux atrm command deletes the scheduled jobs, identified by their job number.
[Use enter & ^D]
servcie : atd
Batch command is also a part of at command , but it executes job when system load is less. batch command is used to schedule a one-time task to be executed.
-----------------------------------------------------------------------------------------------
Crontab :
Crond is a daemon that executes scheduled commands.
SERVICE : crond
FILES :
/var/spool/cron/ : here files are created for separate users including root.
/etc/crontab :
/etc/cron.deny : Restrict users from using crontab. not need to restart crond. because it everytime reads these files when user requests.
]# crontab -l [List cron job file for current user]
]# crontab -l -u procopania [Display cron job file for user procopania]
]# crontab -e [Edits cron job file for current user]
]# crontab -e -u procopania [Edits cron job file for user procopania]
#MIN (0-59) HOUR (0-23) DoM (1-31) MONTH (1-12) DoW (0-7) CMD
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
You can schedule multiple instances in the min, hour, dom etc. columns using a ',' as a separator. For example, to run a job at 9:30PM on the 1st and 15th of each month, the syntax would be:
30 21 1,15 * * <JOB TO RUN>
Examples: In hours field I specified 4-7, Here it will include 4th,5th,6th and 7th hours.
And 5,7 includes 5th and 7th hour. * includes all. For example, "0-23/2" can be used in the hours field to
specify command execution every other hour ( I.e. "0,2,4,6,8,10,12,14,16,18,20,22").
To write the time to the console every hour on the hour, enter:
0 * * * * echo The hour is `date` . >/dev/console
Other than this 8 special strings may appear :
string meaning
------ -------
@reboot Run once, at startup.
@yearly Run once a year, "0 0 1 1 *".
@annually (same as @yearly)
@monthly Run once a month, "0 0 1 * *".
@weekly Run once a week, "0 0 * * 0".
@daily Run once a day, "0 0 * * *".
@midnight (same as @daily)
@hourly Run once an hour, "0 * * * *".
Note : It will execute @ 00:00 for most of the keywords.
]# crontab -r [Delete cron job file for current user]
]# crontab -r -u procopania [Delete cron job file for user procopania]
If you want to send email to specific ID then :
vi /etc/crontab
MAIL="ramesh" Or "mail@example.com" Or ""
OTHER DIRs :
/etc/anacrontab
/etc/cron.d
/etc/cron.daily
/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly
=============================
The crontab command submits, edits, lists, or removes cron jobs.
This command is a command and script schedular.
It runs task scheduling daily,hourly,weekly,monthly, etc.
It also allow users to setup their own schedules.
Example : We uses this command for system auditing ; running backup scripts.
Service : crond
It runs
]# crontab -l -- Lists cron jobs for user himself.
]# crontab -lu proco -- Lists cron jobs for user proco (Only root can execute this command).
]# crontab -eu proco -- Edits user proco's cron file stored at "/var/spool/cron/proco".
]# crontab -ru proco -- Removes cron jobs for user himself.
Format :
MIN HOURS DAYOFMONTH MONTH WEEKDAY COMMAND
(0-59) (0-23) (1-31) (1-12) (0-6 0=SUN) /vz/backup/vzbackup.sh >/dev/null 2>&1
Eg. :
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
Here, we dump data using above "vzbackup.sh" script. Crontab will execute this script daily at 21'st hour of the day.
An * (asterisk), meaning all allowed values. To run a job every hour, specify an asterisk in the hour field.
To write the time to the console every hour on the hour, enter:
0 * * * * echo The hour is `date` . >/dev/console
IMP Files/Dir for crontab :
File:/etc/crontab -- This file contains few directories as below. Script placed in a specific directory will execute according.
File:/var/spool/cron/{root,prem,etc} -- This directory contains separate file for separate user. its a schedular file as below.
File:/etc/cron.deny -- Specifies a list of users denied access to the crontab command.
[root@tlv1 etc]# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/
# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly
---------------------------------------------------
[root@tlv1 ~]# cat /var/spool/cron/root
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
---------------------------------------------------
Example:
Please set this cron to run every day at 11.55pm.
http://experiencesilk.com/duniya_dekhegi/cron_winners.php
Ans:
[root@experiencesilk cron]# cat root
55 23 * * * /usr/bin/php -q /var/www/html/duniya_dekhegi/cron_winners.php
=======================================
at command :
The Linux “at” command used for scheduling jobs. But “at” command can set the job run only once. The “at” daemon can be used to run a command or script of your choice. From the command line, you can run the “at” time command to start a job to be run at a specified time. That time can be now; in a specified number of minutes, hours, or days; or at the time of your choice. Spool area for at command is /var/spool/at/ directory. For normal users, permission to use at command is determined by the file /etc/at.deny. The file /etc/at.deny is checked, every user name not mentioned in it is then allowed to use at.
SYNTAX :
]# at <time>
Here, time format can be :
now
midnight - (12:00AM)
noon - (12:00PM)
teatime - (4:00PM)
14:23 (24 hours format) OR 02:23PM (12 hours format)
now + 05/03/13 - Its MMDDYY format. Here date is 3rd May, 2013. (now = at same time)
now + 10 minutes
now + 2 hours
now + 1 day - After 24 hours.
now + 1 week - After 7 days.
3:00 05/03/13 - On specified date and time.
The Linux atq command lists the user’s pending jobs, unless the user is the superuser; in that case, everybody’s jobs are listed. The format of the output lines (one for each job) is: Job number, date, hour, job class.
The Linux atrm command deletes the scheduled jobs, identified by their job number.
[Use enter & ^D]
servcie : atd
Batch command is also a part of at command , but it executes job when system load is less. batch command is used to schedule a one-time task to be executed.
-----------------------------------------------------------------------------------------------
Crontab :
Crond is a daemon that executes scheduled commands.
SERVICE : crond
FILES :
/var/spool/cron/ : here files are created for separate users including root.
/etc/crontab :
/etc/cron.deny : Restrict users from using crontab. not need to restart crond. because it everytime reads these files when user requests.
]# crontab -l [List cron job file for current user]
]# crontab -l -u procopania [Display cron job file for user procopania]
]# crontab -e [Edits cron job file for current user]
]# crontab -e -u procopania [Edits cron job file for user procopania]
#MIN (0-59) HOUR (0-23) DoM (1-31) MONTH (1-12) DoW (0-7) CMD
41 21 * * * /vz/backup/vzbackup.sh >/dev/null 2>&1
You can schedule multiple instances in the min, hour, dom etc. columns using a ',' as a separator. For example, to run a job at 9:30PM on the 1st and 15th of each month, the syntax would be:
30 21 1,15 * * <JOB TO RUN>
Examples: In hours field I specified 4-7, Here it will include 4th,5th,6th and 7th hours.
And 5,7 includes 5th and 7th hour. * includes all. For example, "0-23/2" can be used in the hours field to
specify command execution every other hour ( I.e. "0,2,4,6,8,10,12,14,16,18,20,22").
To write the time to the console every hour on the hour, enter:
0 * * * * echo The hour is `date` . >/dev/console
Other than this 8 special strings may appear :
string meaning
------ -------
@reboot Run once, at startup.
@yearly Run once a year, "0 0 1 1 *".
@annually (same as @yearly)
@monthly Run once a month, "0 0 1 * *".
@weekly Run once a week, "0 0 * * 0".
@daily Run once a day, "0 0 * * *".
@midnight (same as @daily)
@hourly Run once an hour, "0 * * * *".
Note : It will execute @ 00:00 for most of the keywords.
]# crontab -r [Delete cron job file for current user]
]# crontab -r -u procopania [Delete cron job file for user procopania]
If you want to send email to specific ID then :
vi /etc/crontab
MAIL="ramesh" Or "mail@example.com" Or ""
OTHER DIRs :
/etc/anacrontab
/etc/cron.d
/etc/cron.daily
/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly
=============================
