How to use Screen

Screen is a handy tool for creating SSH sessions that withstand network failures as well as for making SSH terminals containing multiple sessions.

To start a screen session use the command:


You can also give the session a name using the command

screen -S <session name>

To detach from a running screen session use the command:

Ctrl+A d

To list screen sessions use the command:

screen -ls

To resume a screen session use the command:

screen -r


How To Use Linux Screen.

How to cleanly remove Exim 4 on Ubuntu

Run the following command:

apt-get remove exim4 exim4-base exim4-config exim4-daemon-light

All your configs stay on the server so that you can easily get mailing running again by installing it:

apt-get install exim4


exim – How to cleanly remove Exim4 mail server on Ubuntu – Stack Overflow.

How to prevent execessive scraping on Website on Ubuntu Server

Add rules as follows:

iptables -A INPUT -p tcp --syn --dport 80 -m connlimit\
 --connlimit-above 15 --connlimit-mask 32 -j REJECT \
 --reject-with tcp-reset 

This will reject connections above 15 from one source IP.

iptables -A INPUT -m state --state RELATED,ESTABLISHED \
-m limit --limit 150/second --limit-burst 160 -j ACCEPT  

In this 160 new connections (packets really) are allowed before the limit of 150 NEW connections (packets) per second is applied.

Note: if your server runs UFW (Uncomplicated Firewall), then you shouldn’t run the commands directly. Instead, you need to replace INPUT with ufw-before-input in each line and put the lines in the file /etc/ufw/before.rules. Afterwards, restart UFW using the following command:

sudo service ufw restart


Limit max connections per IP address and new connections per second with iptables – Unix & Linux Stack Exchange.

How to remove all iptables rules

Create a file /root/fw.stop with the following content:

echo "Stopping firewall and allowing everyone..."
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT

Make it executable and then run it on the terminal.


An Introduction to tmux

Have you ever felt the discomfort of having to log in twice into a server so you can run two applications simultaneously? Have you wondered if there could be an easier way? Or are you looking for an easy way to start a long process on a server, detach from it, and connect back to the same session from a different client? Well, there’s a solution for all your worries. It’s called tmux! tmux allows you split a terminal into several subsections. It also allows you start a session over ssh and log out while the session keeps running, then log in via ssh on a possibly different machine and resume your session. So, the client becomes more irrelevant. I’ll discuss how to do a few things using tmux.

How to start a new tmux session run the following

tmux new -s session-name

or run the following

tmux new

It’s recommended to use the first format as it gives your sessions more meaningful names.

To detach from a session, run the following:

Ctrl-b d

or run the following

tmux detach

To list sessions, use the command

tmux ls

Note that tmux uses Ctrl-b as a prefix for its operations by default. This can be changed though as tmux is highly configurable.

To attach to an existing session use the following:

tmux a

This attaches to the first available session. You can also use the following:

tmux a -t session-name

To attach to a named session.

When logged in to a session, you can split the window into panes.

To split the window vertically, use the following command:

Ctrl-b %

To split it horizontally use the command:

Ctrl-b "

To switch pane, use the command

Ctrl-b arrow key

To resize a pane use the following command:

Hold Ctrl-b, then hold an arrow key

To scroll up a page on OS X, press Ctrl-b then [. This will put you in scroll mode. You can then use arrow keys to go up and down. To move page by page while in scroll mode, using PageUp and PageDown keys. On a laptop without PageUp key, you can simulate it by pressing Cmd-Up Arrow. To exit scroll mode press q.

To kill or delete a session use the command:

tmux kill-session -t myname

Some helpful resources on tmux can be found at:

dayid’s screen and tmux cheat sheet.

tmux Tutorial – Split Terminal Windows Easily.

A tmux Primer.

Breathing in during Front Crawl

Hello folks,

In my last post I discussed the lessons I learnt about breathing out in water. Today I’m going to talk about breathing in air while doing a front crawl.

When breathing in, some beginners, myself included, tend to raise our heads to take in air. This is wrong as it causes the legs to sink. You see, the body can be thought of as a see-saw. When one part goes up on water the other part tends to go down.

So, how should one breathe out while swimming with front crawl? The best way which I discovered in my last lesson is to turn sideways with the neck remaining as parallel to your trunk as possible at appropriate moments. So what’s an appropriate moment? I’ll give an example. Suppose you want to breath out to your right side. So, you push and glide in the pool, then start kicking, and then you starting making hand strokes. You wait until your left hand is stretched straight in front of you while your right hand is stretched straight backwards. This is the perfect time to tilt your head to the right and take in some air.

Also, it’s important to keep kicking while breathing in otherwise you generally begin to sink.