00 - Linux Commands

Set the Target IP Address to the $ip system variable
     # export ip=192.168.1.100

Find the location of a file
     # locate sbd.exe

Search through directories in the $PATH environment variable
     # which sbd

Find a search for a file that contains a specific string in it’s name
     # find / -name sbd\*

Show active internet connections
     # netstat -lntp

Change Password
     # passwd

Verify a service is running and listening
     # netstat -antp |grep apache

Start a service
     # systemctl start ssh
     # systemctl start apache2

Unzip a gz file
     # gunzip access.log.gz

Unzip a tar.gz file
     # tar -xzvf file.tar.gz

Search command history
     # history | grep phrase\_to\_search\_for

Have a service start at boot
     # systemctl enable ssh

Stop a service
     # systemctl stop ssh

Download a webpage
     # wget [www.cisco.com](http://www.cisco.com)
     
Open a webpage
     # `curl www.cisco.com

String manipulation
     Count number of lines in file
     # wc index.html

Get the start or end of a file
     # head index.html tail index.html

Extract all the lines that contain a string
     #grep "href=" index.html

Cut a string by a delimiter, filter results then sort
     # grep "href=" index.html | cut -d "/" -f 3 | grep "\\." | cut -d '"' -f 1 | sort -u

Using Grep and regular expressions and output to a file
     # cat index.html | grep -o 'http://\[^"\]\*' | cut -d "/" -f 3 | sort –u > list.txt

Use a bash loop to find the IP address behind each host
     # for url in $(cat list.txt); do host $url; done

Collect all the IP Addresses from a log file and sort by frequency
     # cat access.log | cut -d " " -f 1 | sort | uniq -c | sort -urn

IPTables deny traffic to ports except for Local Loopback
           # iptables -A INPUT -p tcp --destination-port 13327 \\! -d $ip -j DROP
           # iptables -A INPUT -p tcp --destination-port 4444 \\! -d $ip -j DROP