Sunday, September 25, 2011

Speeding up Bash Profile Load Time

I started noticing a considerable delay whenever opening a new terminal or connecting to another server. After profiling my Bash profile with a few time commands, I discovered that the slowest part was the loading of the completion file:
$ time  ~/.bash/.bash_completion

real    0m0.457s
user    0m0.183s
sys     0m0.276s
The Bash completion script I use is from I found that there is an existing bug for this issue #467231: bash_completion is big and loads slowly; load-by-need proposed and someone has submitted a script to speed up Bash completion load time called

This is a one-time script, which only needs to be run when you install your Bash completions or modify them. It loads your completions and moves the completion functions out of the script and into a separate directory. They are only loaded when needed. This speeds up the load time considerably and new terminal windows open up instantly!

$ time  ~/.bash/.bash_dyncompletion

real    0m0.020s
user    0m0.018s
sys     0m0.002s
You can visit my GitHub dotfiles repository for the latest version of my Bash profile.

Saturday, September 17, 2011

Faster SSH with Multiplexing

OpenSSH allows you to speed up multiple SSH connections to the same server using "multiplexing". The first connection acts as the "master" and any other connections reuse the master instance's network connection rather than initiating new ones.

In order to set this up add the following to your ~/.ssh/config file:

Host *
ControlMaster auto
ControlPath /tmp/%r@%h:%p
ControlMaster auto will use a master if one exists, or start a master otherwise. ControlPath is the path to the control socket used for connection sharing. %r, %h and %p are replaced with your username, host to which you are connecting and the port respectively.

In addition, you may want to add Ciphers arcfour in order to use the arcfour cipher which is faster than the default (aes128-cbc). The transfer rate of arcfour is about 90 MB/s, aes128-cbc is about 75 MB/s and the slowest is 3des-cbc, at 19 MB/s.