|
Automating Tasks in Linux using Cron Linux has a powerful task scheduler called Cron. Cron will allow you to
run commands automatically at times specified by you. Cron is similar to the
task scheduler you find in Windows. To keep track of the schedules and tasks
it has to run, Cron requires a file called Crontab (CRON TABle). All the
Cron schedules and tasks should be stored in this table. The Crontab files
cannot be directly edited. You can add or delete entries in the crontab file
using the crontab command.
What's Cron and Crontab ?
You must be wondering what the difference between cron and crontab or wether
they are the same. Cron is a process or program which wakes up every minute
and looks for jobs it has to execute at that moment. Crontab is the list of
jobs and times at which they have to execute.
Crontab Format:
Each entry in Crontab has at least 6 fields separated by a single space.
Field 1 Minute Range of Values : 0-59 Field 2 Hour Range of Values : 0-23
Field 3 Day Range of Values : 1-31 Field 4 Month Range of Values : 1-12
Field 5 Day of week Range of Values : 0-6 (Sunday being 0) Field 6 Command
to Execute
Now let's see how to make a crontab entry. Let's say you want to run a
script backup.sh every day at 6:00pm.The entry would look like this:
0 18 * * * /home/user/backup.sh
The asterisk (*) is used to indicate that every instance of the particular
time period will be used (i.e. every hour, every weekday, etc.). I've used
to full path to the script /home/user/backup.sh instead of just using
backup.sh. This is because cron runs as root, you should fully qualify your
path names to any scripts that will be run. Let's see some more examples :
* Let's run the script printinvoices.sh every sunday at 12:45pm.
45 12 * * 0 /home/account/printinvoices.sh
* How about clearaccount.sh every month beginning at 1:32am ?
21 1 1 * * /home/accont/clearaccount.sh
* Let's see how to schedule a task to run only on weekdays(monday to friday)
0 10 * * 1-5 /home/account/cleartemp.sh
Adding and Editing Entries in Crontab and Now that you know how crontab
entries are formated, it's time to put some of your entries into the crontab
list. To do this, you can use the crontab command. By specifying the -e
option, you'll be taken to the default text editor to add and edit your
crontab list. [crontab -e]
Another method of manipulating your crontab entries is to create and save a
text file with your crontab entries. You can load your list into crontab by
using the following command: [crontab mycrontablist] where mycrontablist is
the file containing your entries.
Viewing Crontab: [crontab -l]
You can view your current crontab list by specifying the -l option. Issuing
this command will print out a list of all your current jobs in the crontab
list
Removing Crontab: [crontab -r]
The -r option removes your current crontab file. Issuing this command will
empty the contents of the current user's crontab file
Output from cron
Usually the output of cron gets mailed to the owner of the process or the
person or email id specified in the MAILTO variable. To set the MAILTO
variable, you'll have to add the following command to the top of your
crontab : MAILTO="your_email_address@domain.com"
If you have a command that is run frequently, and you don't want the output
to be emailed each time, you can redirect the output to a log file cmd >>
log.file, so your job would be something like this.
0 18 * * * /home/user/backup.sh>>log.file
If you don't want any output at all, you can redirect the output to a null
file : cmd>>/dev/null
0 18 * * * /home/user/backup.sh>>/dev/null
About the Author
Vinu Thomas is a consultant on Web design and Internet Technologies. His
website is http://www.vinuthomas.com.
You can read more articles on Linux @
http://www.vinuthomas.com/sections-listarticles-6.html
Additional Check linux version Resources
LinuxDevices.com -- your embedded Linux resource
Comprehensive information and resources on using Linux in embedded applications. This site provides embedded Linux news, articles, events, links, jobs, polls, ...
FrontPage - DOOM III GNU/Linux FAQ
ATI's Proprietary Linux Drivers (fglrx) version 3 ... check the Linux Gamers' FAQ for any issue not covered here ... search on Google...
LinuxGames - For the People
Rak also previously stated that the Linux version is running well, but the distribution method ... Check out the cameo that I included!
Mathematica Platform Availability and Technical Requirements
Sign up for our newsletter: Mathematica Platform Availability. Industry-leading software engineering at Wolfram Research delivers rapid support for the latest operating systems and ...
Linux, unix
Recognize which WWW server has been used, Recognize which SSL enabled WWW server has been used, Response time of the WWW server, Response time of the SSL enabled WWW server, Check ...
Mozilla 1.x Releases
...linux.tar.gz - Sun Contributed Build for Java Desktop for Linux version 2 and 3 (README) (MD5SUM) tar.bz2 format: French Solaris x86, check...
LinuxQuestions.org - Check version of program from urpmi - where Linux
LinuxQuestions.org offers a free Linux forum where Linux newbies can ask questions and Linux experts can offer advice. Topics include security, installation, networking and much more. ... ...
Maltese spell checker
Visit the link for details.
iForce VPN/Firewall Appliance
Appliance GUI interface for configuration and management, a hardened version of Linux and Check Point VPN-1/Firewall-1 NG software includes redundant psu and dual processor capability. VPN ...
Linux Version Control & Configuration Management Tools
Linux Version Control & Configuration Management Tools ... Most Linux distributions come with an rdist client. Check for "man rdist".
Tech Blogs on ZDNet | blogs.ZDNet.com
... The evils of self check-in kiosks ... both Windows XP Pro and Redhat Linux on my notebook computer ... Unlike other releases, this version actually has a couple changes that ...
[LUG] Star office - US spell check default,
...Hi, I have noticed that my Star office spell check is stuck in US english and I have.....Linux and will always be better, One last point is it possible to detect which client.....Linux ...
freshmeat.net: Welcome to freshmeat.net
This version is based on version 1.10 of simple ... Tunnel 0.60 - Linux ACPI client 0.09 - CCTunes 0.7 - Check Website 1.23 - dvbd 0.7.6 - Linux...
MythTV
... else you won't get the updated version for this release ... a bugfix/minor feature release. Check the changelog for specifics ... the DVB drivers in Linux and is capable of receiving ...
No Title.
...fixed dependency cheking for packages that are installed at the same time - fixed version.....linux.prov won't print provides info for symlinks which point to libraries w/ ...
Other Recommended Check linux version Links
Linux backup tar
Linux oracle cluster
Access cluster free linux
Cluster linux manegment sof...
Bladecenter linux cluster
Hpc linux cluster
Linux cluster software
Download red hat linux 9
How to install red hat linu...
Red hat linux 9 tutorial
Linux help desk software
Help desk linux
Blogspot.com desk help linu...
Suse linux help
Mandrake linux help
|
