Posts Tagged ‘jambo’

How to add a range of virtual IPs to a CentOS and Fedora Linux server

Monday, July 18th, 2011

Recently I had the task to add a range of few IP addresses to as a virtual interface IPs.

The normal way to do that is of course using the all well known ifconfig eth0:0, ifconfig eth0:1 or using a tiny shell script which does it and set it up to run through /etc/rc.local .

However the Redhat guys could omit all this mambo jambo and do it The Redhat way TM 😉 by using a standard method documented in CentOS and RHEL documentation.
Here is how:

# go to network-script directory[root@centos ~]# cd /etc/sysconfig/network-scripts
# create ifcfg-eth0-range (if virtual ips are to be assigned on eth0 lan interface[root@centos network-scripts]# touch ifcfg-eth0-range

Now inside ifcfg-eth0-range, open up with a text editor or use the echo command to put inside:

IPADDR_START=192.168.1.120
IPADDR_END=192.168.1.250
NETMASK=255.255.255.25
CLONENUM_START=0

Now save the /etc/sysconfig/network-scripts/ifcfg-eth0-range file and finally restart centos networking via the network script:

[root@centos network-scripts]# service network restart

That’s all now after the network gets reinitialized all the IPs starting with 192.168.1.120 and ending in 192.168.1.250< will get assigned as virtual IPs for eth0 interface
Cheers 😉

How to add cron jobs from command line or bash scripts / Add crontab jobs in a script

Saturday, July 9th, 2011

I’m currently writting a script which is supposed to be adding new crontab jobs and do a bunch of other mambo jambo.

By so far I’ve been aware of only one way to add a cronjob non-interactively like so:

                 linux:~# echo '*/5 * * * * /root/myscript.sh' | crontab -

Though using the | crontab – would work it has one major pitfall, I did completely forgot | crontab – OVERWRITES CURRENT CRONTAB! with the crontab passed by with the echo command.
One must be extremely careful if he decides to use the above example as you might loose your crontab definitions permanently!

Thanksfully it seems there is another way to add crontabs non interactively via a script, as I couldn’t find any good blog which explained something different from the classical example with pipe to crontab –, I dropped by in the good old irc.freenode.net to consult the bash gurus there 😉

So I entered irc and asked the question how can I add a crontab via bash shell script without overwritting my old existing crontab definitions less than a minute later one guy with a nickname geirha was kind enough to explain me how to get around the annoying overwridding.

The solution to the ovewrite was expected, first you use crontab to dump current crontab lines to a file and then you append the new cron job as a new record in the file and finally you ask the crontab program to read and insert the crontab definitions from the newly created files.
So here is the exact code one could run inside a script to include new crontab jobs, next to the already present ones:

linux:~# crontab -l > file; echo '*/5 * * * * /root/myscript.sh >/dev/null 2>&1' >> file; crontab file

The above definition as you could read would make the new record of */5 * * * * /root/myscript.sh >/dev/null be added next to the existing crontab scheduled jobs.

Now I’ll continue with my scripting, in the mean time I hope this will be of use to someone out there 😉