A cron is a utility that allows tasks to automatically run in the background of the system at regular intervals by use of the cron daemon. Crontab (CRON TABle) is a file which contains the schedule of cron entries to be run and at what times they are to be run. This can be quite useful. For example, you may have a personal temporary directory that you wish to be cleaned out once a day to keep your quota from being exceeded. This is where cron scheduling comes in to play. Not all systems allow for a cron schedule to be setup. You need to see your system administrator to see if it is available on your system.

Start/Stop/Restart cron service in Redhat/Fedora/CentOS

If you are using Redhat/Fedora/CentOS Linux login as root and use the following commands.

Start cron service
To start cron service, enter:

# /etc/init.d/crond start

Or

# service crond start

Stop cron service
To stop cron service, enter:

# /etc/init.d/crond stop

Or

# service crond stop

Restart cron service
To restart cron service, enter:

# /etc/init.d/crond restart

Or

# service crond restart

Start/Stop/Restart cron service in Debian/Ubuntu

If you are using Debian/Ubuntu Linux login as root and use the following commands.

Start cron service
To start cron service, enter:

# sudo /etc/init.d/cron start

Or

# sudo service cron start

Stop cron service
To stop cron service, enter:

# sudo /etc/init.d/cron stop

Or

# sudo service cron stop

Restart cron service
To restart cron service, enter:

# sudo /etc/init.d/cron restart

Or

# sudo service cron restart

The post How To Start/Stop/Restart Cron Service In Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

By default iptables firewall stores its configuration at /etc/sysconfig/iptables file. Type the following command to see its

# cat /etc/sysconfig/iptables

Or

# iptables -L

Temporarily delete all the firewall rules

At first, create flush.iptables script with following command

# vi flush.iptables

Add the following content

#!/bin/sh
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

Finally, run flush.iptables script with the following command

# sh flush.iptables

After running flush.iptables script, if you restart the iptables, you’ll see all the default rules again. So, flush is only temporary.

Permanently remove all the default firewall rules

Step 1. Flush all these rules temporarily, as we discussed above.
Step 2. Saving firewall rules to /etc/sysconfig/iptables. Type the following command

# /etc/init.d/iptables save

Or

# iptables-save > /etc/sysconfig/iptables

The post How To Flush/Remove All Iptables Rules In Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.