tmux 2.0 and tmux 2.3 installation steps for Ubuntu. Or build from tmux source v2.5 for Ubuntu and CentOS.

tmux__CentOS__build_from_source.sh

# Steps to build and install tmux from source.
# Takes < 25 seconds on EC2 env [even on a low-end config instance].

VERSION=2.7
sudo yum -y remove tmux
sudo yum -y install wget tar libevent-devel ncurses-devel
wget https://github.com/tmux/tmux/releases/download/${VERSION}/tmux-${VERSION}.tar.gz
tar xzf tmux-${VERSION}.tar.gz
rm -f tmux-${VERSION}.tar.gz
cd tmux-${VERSION}
./configure
sudo make install
cd -
sudo rm -rf /usr/local/src/tmux-*
sudo mv tmux-${VERSION} /usr/local/src

## Logout and login to the shell again and run.
## tmux -V

tmux__Ubuntu__build_from_source.sh

# Steps to build and install tmux from source on Ubuntu.
# Takes < 25 seconds on EC2 env [even on a low-end config instance].
VERSION=2.7
sudo apt-get -y remove tmux
sudo apt-get -y install wget tar libevent-dev libncurses-dev
wget https://github.com/tmux/tmux/releases/download/${VERSION}/tmux-${VERSION}.tar.gz
tar xf tmux-${VERSION}.tar.gz
rm -f tmux-${VERSION}.tar.gz
cd tmux-${VERSION}
./configure
make
sudo make install
cd -
sudo rm -rf /usr/local/src/tmux-*
sudo mv tmux-${VERSION} /usr/local/src

## Logout and login to the shell again and run.
## tmux -V

tmux_install.sh

##########################################################################################
##### Please check the installation from source, which is easy and fast.
##########################################################################################
# tmux v2.3 installation steps for Ubuntu [various OS versions]
sudo apt-get update -yqqu
sudo add-apt-repository -yu ppa:pi-rho/dev
sudo apt-get update -yqqu
sudo apt-get install -yqqu python-software-properties software-properties-common
sudo apt-get install -yqq tmux-next=2.3~20160913~bzr3547+20-1ubuntu1~ppa0~ubuntu16.04.1
# sudo apt-get install -yqq tmux-next=2.3~20160913~bzr3547+20-1ubuntu1~ppa0~ubuntu15.10.1
# sudo apt-get install -yqq tmux-next=2.3~20160913~bzr3547+20-1ubuntu1~ppa0~ubuntu15.04.1
# sudo apt-get install -yqq tmux-next=2.3~20160913~bzr3547+20-1ubuntu1~ppa0~ubuntu14.04.1
# sudo apt-get install -yqq tmux-next=2.3~20160913~bzr3547+20-1ubuntu1~ppa0~ubuntu12.04.1
tmux-next -V

# tmux v2.0 installation steps for Ubuntu 14.04 (Trusty Tahr)
tmux -V
sudo apt-get update -yqqu
sudo apt-get install -yqqu python-software-properties software-properties-common
sudo add-apt-repository -yu ppa:pi-rho/dev
sudo apt-get update -yqqu
sudo apt-get install -yqqu tmux
# sudo apt-get install -yqqu tmux=2.0-1~ppa1~t
tmux -V

# tmux v1.9 installation steps for Ubuntu 14.04 (Trusty Tahr)
sudo apt-get update -yqqu
sudo apt-get install -yqqu python-software-properties software-properties-common
sudo add-apt-repository -yu ppa:pi-rho/dev
sudo apt-get update -yqqu
sudo apt-get install -yqqu tmux=1.9a-1~ppa1~t
tmux -V

# On Ubuntu 12.04 (Precise Pangolin), step 5 would be: sudo apt-get install -y tmux=1.9a-1~ppa1~p
# On Ubuntu 13.10 (Saucy Salamander), step 5 would be: sudo apt-get install -y tmux=1.9a-1~ppa1~s

Thanks!

having trouble to configure $PWD to start on the new session while splitting on version 2.5 anyone?

Thanks :)

Thank you for CentOS steps!