Some useful commands to Manage/Monitor Servers

These commands are mainly for rpm based linux servers like CentOS etc.. May be some commands works in ubuntu servers etc...

Command to find out total established connections, closing connection, TIME_WAIT and much more.

netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n

Sample Output:

1 established
1 Foreign
5 LISTEN
16 TIME_WAIT
19 ESTABLISHED

Dig out more information about a specific ip address

netstat -nat |grep {IP-address} | awk '{print $6}' | sort | uniq -c | sort -n

2 LISTEN
4 FIN_WAIT1
4 ESTABLISHED
7 TIME_WAIT

To print list of all unique IP address connected to server, enter:

netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | uniq

To print total of all unique IP address, enter:

netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | uniq | wc -l

Find Out If Box is Under DoS Attack or Not

If you think your Linux box is under attack, print out a list of open connections on your box and sorts them by according to IP address, enter:

netstat -atun | awk '{print $5}' | cut -d: -f1 | sed -e '/^$/d' |sort | uniq -c | sort -n

Command to list the connections to port 80:

netstat -alntp | grep :80

To check the number of connections to port 80:

netstat -alntp | grep :80 | wc -l

Command To Find Out Top 10 CPU Consuming Process

ps -auxf | sort -nr -k 3 | head -10

Command To Find Out The Top 10 Memory Consuming Process

ps -auxf | sort -nr -k 4 | head -10

An useful command to list connections to a particular port with its proccess id.

For eg: Port 8080

lsof -w -n -i tcp:8080

Command to remove a running process.
For eg: a proccess with PID 8457

kill -9 8457

Linux Screen Command

Steps


- Create a screen using the command

screen -S geopc

- Close the shell without logout


- Open a new shell and type

screen -ls

Sample Output:

There are screens on:
16921.joemon (Dead ???)
3981.name (Attached)
5002.geopc (Attached)
Remove dead screens with 'screen -wipe'.
3 Sockets in /tmp/screens/S-root.


- You can login to that screen using the command screen -r 'screen name'

screen -r 5002.geopc

To attach a scree that is already attached with the following command:

screen -x -R

You can add your commands as comments!... :)