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Useful Linux commands

Tue May 9, 2017

Below are some useful Linux commands for penetration testing, target reconaissance and capability assessment. Use them for good, not for evil.


user@host:~$ traceroute <target>

user@host:~$ traceroute google.com
traceroute to google.com (, 24 hops max, 52 byte packets
 1  192-168-1-110.x.com (  9.403 ms  7.301 ms  3.264 ms
 2 (  47.823 ms  3.649 ms  2.436 ms
 	... etc ...


user@host:~$ whois [-h whois_server] <name>

user@host:~$ whois google.com
Whois Server Version 2.0

Domain names in the .com and .net domains can now be registered
with many different competing registrars. Go to http://www.internic.net
for detailed information.

Aborting search 50 records found .....
	... etc ...


user@host:~$ nslookup <target>

user@host:~$ nslookup google.com

Non-authoritative answer:
Name:	google.com
Name:	google.com
Name:	google.com
	... etc ...


user@host:~$ dig [@server] <name> [record_type]
user@host:~$ dig [@server] <domain> -t IXFR=<N>

user@host:~$ dig google.com MX
; <<>> DiG 9.10.3-P4-Ubuntu <<>> google.com MX
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61593
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1

; EDNS: version: 0, flags:; udp: 4096
;google.com.			IN	MX

google.com.		60	IN	MX	20 alt1.aspmx.l.google.com.
google.com.		60	IN	MX	30 alt2.aspmx.l.google.com.
google.com.		60	IN	MX	40 alt3.aspmx.l.google.com.
google.com.		60	IN	MX	50 alt4.aspmx.l.google.com.
google.com.		60	IN	MX	10 aspmx.l.google.com.
	... etc ...

Dump the ARP table of a SNMP server:

user@host:~$ snmpwalk -v 2c -c <community> <server> ip.ipNetToMediaTable.ipNetToMediaEntry.ipNetToMediaPhysAddress > arptable.dump

Show all TCP port 80 packets going to or from the specified IP:

user@host:~$ tcpdump [-i tap0] -n tcp and port 80 and host

Enumerate local users:

user@host:~$ cat /etc/passwd
	... etc ...

user@host:~$ finger
Login     Name       Tty      Idle  Login Time   Office     Office Phone
root      root      *pts/0          March  19 11:13 (

user@host:~$ who
root     pts/0        2017-05-09 11:13 (

user@host:~$ w
 11:18:56 up 169 days,  11:18,  1 user,  load average: 0.00, 0.00, 0.00
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0      11:13    0.00s  0.02s  0.00s w

Enumerate remote users:

user@host:~$ finger @<remote>

Scan the target’s specified port range:

user@host:~$ echo "" | nc -v -n -w1 <target> <port-range>

Find SetUID or SetGID binaries:

user@host:~$ find / -type f \( -perm -4000 -o -perm -2000 \) -print

Mounting a Samba drive:

user@host:~$ smbmount //<target>/<share> <mountpoint> -o username=<username>

user@host:~$ smbmount //$ /mnt/target -o username=administrator

Find any open Samba shares:

user@host:~$ nmap -T4 -v -oA shares --script smb-enum-shares --script-args smbuser=username,smbpass=password -p445 

Add a normal user:

user@host:~$ useradd <name>

Add a root user:

user@host:~$ useradd -o -u 0 <name>

Manual fingerprinting and banner grabbing:

user@host:~$ nc -v 25
user@host:~$ telnet 25

And while at it, grab the SSH server version too (if running):

user@host:~$ nc -v 22
Connection to port 22 [tcp/ssh] succeeded!
SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.1

Fingerprint Samba version too:

user@host:~$ smbclient -L //

Quickly determine if a port is open or closed using just bash:

user@host:~$ (: </dev/tcp/ &>/dev/null && echo "OPEN" || echo "CLOSED"
Start a simple web server, depending on what is installed (python, python3, php or ruby):
user@host:~$ python -m SimpleHTTPServer 80
user@host:~$ python3 -m http.server
user@host:~$ php -S
user@host:~$ ruby -rwebrick -e "WEBrick::HTTPServer.new(:Port => 80, :DocumentRoot => Dir.pwd).start"

Spawn a TTY shell from a limited shell in Linux using Python:

user@host:~$ python -c 'import pty;pty.spawn("/bin/bash")'

Spawn a TTY shell from a limited shell in Linux using Perl:

user@host:~$ perl —e 'exec "/bin/sh";'

Download all documents and images from a web page address:

user@host:~$ wget -A pdf,jpg,png,gif,bmp,doc,docx -m -r -np --convert-links --execute="robots = off" <address>

Encrypt a file using gpg:

user@host:~$ gpg --encrypt --sign -r you@email <filename>

Decrypt a file using gpg:

user@host:~$ gpg -d <filename>

Perform a request to a remote address every 5 seconds (download a file, whatever), until you press CTRL + C:

user@host:~$ while true; do wget <address>; sleep 5; done

Dump all MySQL databases:

user@host:~$ mysqldump --all-databases --all-routines -u root -p > ~/fulldump.sql

Use nikto to scan a host using a proxy server and output fingerprinted info to a file:

user@host:~$ perl nikto.pl -host <ip_or_hostname> -useproxy <proxy_address> -output <filename>

Use wpscan to scan a Wordpress install and output fingerprinted into to a file:

user@host:~$ ruby wpscan.rb --url <address> --enumerate 2> <filename>

Use sqlmap to grab the database banner, if possible:

user@host:~$ ./sqlmap.py --url="<address>" --data="<post-data>" --banner

Grab the HTTP headers:

user@host:~$ curl -LIN <address>

user@host:~$ curl -LIN google.com
HTTP/1.1 200 OK
Date: Tue, 19 March 2017 13:12:48 GMT
Expires: -1
Cache-Control: private, max-age=0
Content-Type: text/html; charset=ISO-8859-1
Server: gws
X-XSS-Protection: 1; mode=block
	... etc ...

Generate a MD5 hash of the specified string:

user@host:~$ echo -n "This is the text" | openssl md5
(stdin)= 4da8333008320dd94d593f3211df63ab

Generate a SHA hash of the specified string:

user@host:~$ echo -n "This is the text" | openssl sha
(stdin)= 0dc9696177e9786de95a1caee349a7a6da70a614

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