Compare two files and list common lines

You can use the awk command to compare two files and show the common ones. Compared to the Linux command “comm”, advantages of using “awk” is it will give output though the files are not sorted.
Syntax :

awk 'NR==FNR{a[$1]++;next} a[$1] ' file1 file2

Eg :

[root@test]# cat A
apple
orange
mango
grape

[root@test]# cat B
mango
banana
grape

[root@test]# awk 'NR==FNR{a[$1]++;next} a[$1] ' A B
mango
grape

Device eth0 does not seem to be present, delaying initialization.

You might have come across this headline, especially if you working with Oracle Virtual box machines, machines those are cloned from previous setups etc.

device

To resolve the issue, just remove the file /etc/udev/rules.d/70-persistent-net.rules and reboot the machine. This file contains the MAC address details associated with the machine. If you don’t want to reboot the machine, run the below command :

udevadm trigger --subsystem-match=net

This command will trigger the rules again.

Enjoy 🙂

Install Oracle JDK

Go to the link : http://www.oracle.com/technetwork/java/javase/downloads/

Accept the license agreement and Download the tar.gz file (eg: jdk -8u65-linux-i586.tar.gz)

Extract the file using the command tar -xzvf jdk-8u65-linux-i586.tar.gz

Copy the extracted directory (In my case jdk1.8.0_65) to the required location say /scratch

alternatives –install /usr/bin/java java /scratch/jdk1.8.0_65/bin/java 20000

alternatives –config java

You can see the list of available java versions and select our installed one by typing the number corresponding to that one.

Run a script at boot time in CentOS 7

By default /etc/rc.local and /etc/rc.d/rc.local are no longer executable in CentOS7 with the new systemd-changes. Follow the below steps to make the script /root/g.sh run at boot time:

1. chmod +x /etc/rc.d/rc.local
2. chmod +x /root/g.sh
2. Mention your script at the bottom of the file /etc/rc.local (/etc/rc.local is a symlink to /etc/rc.d/rc.local)as below :

sh /root/g.sh

Restart and check 🙂

Import certificate and key into jks

1. First create a p12 file and import both the certificate and key into it using openssl.

openssl pkcs12 -export -name theg -in /etc/ssl/certs/theg.crt -inkey /etc/ssl/private/theg.key -out theg.p12

2.Convert the p12 format into jks format using keytool :

keytool -importkeystore -destkeystore theg.jks -srckeystore theg.p12 -srcstoretype pkcs12 -alias theg

Note : Here I used the name theg for my certificates and alias, change it accordingly.