Linux how to

Below command have been tested on Ubuntu OS.
Remove a directory:
rmdir python

Remove a non empty directory:
rm -rf pythonscripts

To reach to your home directory:
cd ~

To create a path shortcut in linux:
Create a global variable:
export variablename=”path”
Use in the command for example:
cd $variablename

To check global variable:

printenv

To extract the tar file use following command:
tar -xf

To extract file to a new directory use following command:
mkdir techsupport && tar -xf techsupport.tgz -C techsupport

Search pattern with grep:
grep “pattern to search”

Show few line after the matched pattern:
grep -A “pattern to search”
grep -A4 “:packet” monitor.log

Search all file inside a directory and sub directory:
grep-R “pattern to search” *

To get list of installed software:
dpkg -l

To check the version of a software:
dpkg -l syslog-ng

To uninstall one software:
apt-get –purge remove

To check if a software is installed or not:
apt-cache policy openssl

To find a directory/file name in linux:
find / -name Desktop

To check Linux is listening on which ports:
netstat

To get folder size:

du -sh /var/

To get disk space:

df -h

To get file system type:

df -T

To get all folder size:

du

To capture traffic using tcpdump:

tcpdump -i any host 62.239.180.185 and  port 18184

Root password: By default ubuntu root password is not set. You need to set the root password use following command to set root password

sudo passwd root
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