morteza-mori

All connections to server
netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n
All connection States
netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n
Limit HTTP connections to 20 sessions
iptables -I INPUT -p tcp --syn --dport 80 -m connlimit --connlimit-above
20 --connlimit-mask 24 -j DROP
Checking how many connections to 80
netstat -n | grep :80 |wc -l

morteza-mori

Users & Groups
Group file: /etc/group
Add User:
adduser USER
New Group:
groupadd GROUP
newgrp GROUP
Account numbering and important settings: /etc/login.defs
Own a user a folder:
chown -R USER FOLDER

morteza-mori

PostgreSQL
Client: psql
Connect to server: psql -h server.domain.org database user
Connection quit: \q
Connect: sudo -u postgres psql postgres
Create user: sudo -u postgres createuser -D -A -P myuser
Create Database: sudo -u postgres createdb -O myuser mydb
Drop Database: drop database DATABASE ;
Dump Database: pg_dump -Fc -U USER DATABASE > NAME
Restore Database: pg_restore -Fc -j CORE_LIMIT -U USER -d DB OLDDB

morteza-mori

NMAP
Ping with nmap
nmap -sP IP
Port state
nmap --reason HOST
TCP connect() scan—(Nmap -sT )
TCP SYN or half-open scan—(Nmap -sS )
TCP FIN, XMAS, and NULL scans—(Nmap -sF , -sX , -sN )
TCP ACK scan—(Nmap -sA )
TCP idle scan—(Nmap -sI )

morteza-mori

NetCat
Ex: nc -v IP PORT → Connect to the port
Open port and listen: nc -k -l PORT → -k means keep listening
Port scanning: nc -zv IP PORTRANGE
nc -p 31337 -w 5 host.example.com 42
Open a TCP connection to port 42 of host.example.com, using port 31337 as
the source port, with a timeout of 5 seconds:
nc -u host.example.com 53
Open a UDP connection to port 53 of host.example.com
To listen on port PORT and accept:

morteza-mori

Kill TCP connection
tcpkill -9 host google.com
Create IPIP Tunnel:
Linux 1:
# ip tunnel add ipip-Tunnel mode ipip remote 20.0.0.2 local 20.0.0.1
# ifconfig ipip-Tunnel 10.0.0.1/24
Linux 2:
# ip tunnel add ipip-Tunnel mode ipip remote 20.0.0.1 local 20.0.0.2
# ifconfig ipip-Tunnel 10.0.0.2/24
# ip tunnel show

morteza-mori

lsof → List open files.
lsof -i :PORT → Shows networking related port
lsof -i@IP → Shows connections to a specific host
lsof -i -sTCP:LISTEN → Shows listening ports
lsof -i -sTCP:ESTABLISHED → Shows established connections
lsof -u USER → What user opens
lsof DIR → Shows everything interacting with a given DIR
lsof -i :PORT → Shows which process uses the port

morteza-mori

Find all files in home folder with mp3 format
find ~ -iname '*.mp3'
Find all directories with 777 perm
find /var/www -type d -perm 777
Find all files greater than 20M and sort
find / -type f -size +20M -exec ls -lh {} \; 2> /dev/null | awk '{ print
$NF ": " $5 }' | sort -nk 2,2
Find text files that were last modified 60 days ago
find /home/you -iname "*.txt" -mtime -60 -print

morteza-mori

nethogs - iptraf - bmon - iftop - nmon - glances - iostat - iotop - tload - pstree
- httpry​- dhcpdump - mysql-sniffer - p0f - pktstat​- sysdig​- tcptrack ​-
vnstat - goaccess ​- apachetop - whowatch

morteza-mori

According to some problems which happend on servers, it's good idea to use Tmux with RED pane color on servers to avoid problems.

After installing Tmux, put this config in "/etc/tmux.conf" or "~/.tmux.conf": set -g status-bg red
My terminal demonstration:
Green: is my local tmux

Red: is server tmux