Like many people I frequently work on the same project on several computers. This usually results in frequent use of ssh when I forget to commit changes on git, or don't have all the correct software on one computer. Since I don't have a static ip I have been using Dropbox to keep track of the address and then update aliases manually. Today I decided to automate the process and as I know I will forget how I did it, I will record the process here for myself in the future.

Python script

Firstly we need a script which saves an the address as a useful alias:

!/usr/bin/python

import subprocess import os

Read in the ipaddress, hostname and username

command_line = "/sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2| awk '{print $1}'" ipaddress = subprocess.check_output(command_line, shell=True).rstrip("\n") hostname = subprocess.check_output("hostname", shell=True).rstrip("\n") user = subprocess.check_output("/usr/bin/whoami", shell=True).rstrip("\n")

Save results in a dictionary

data = {}

Save aliases in a file

dir_of_script = os.path.dirname(os.path.realpath(file)) alias_file = "ssh-aliases" alias_file = dir_of_script+"/"+alias_file

If file exists read in data

try:
with open(alias_file, "r") as file: for line in file: [alias, syscall] = line.split("=") data[alias.lstrip("alias ")] = syscall.lstrip("'ssh -X ").rstrip("'\n").split("@") data[hostname] = [user, ipaddress] except IOError: data = {hostname : [user, ipaddress]}

Write to the file

with open(alias_file, "w+") as file: for key, val in data.iteritems(): file.write("alias {}='ssh -X {}@{}'\n".format(key, val[0], val[1]))

When run, this will save a file in the current directory ssh-aliases containing an aliases to access the current machine. If a previous entry existed and the ip address has changed then the alias file will be updated.

Dropbox

A simple way to share these aliases between several computers is to use Dropbox. Save the script above as saveIP.py in a directory eyeP of your Dropbox folder.

Crontab

Now we need to ask each computer to automatically run this python script at startup. This can be achieved by adding a crontab job. First run

crontab -e

If this is the first time you have run crontab it will ask you which editor to use. When in doubt, choose the default. Then add the line

@reboot sleep 60 && python ~/Dropbox/eyeP/saveIP.py

editing the path as appropriate. Note that the cronjob sleeps for a minute first, this avoids issues where the ipaddress and username come up blank. I don't know what causes them, but this seems a sensible work around.

Edit profile

Finally we just need to edit ~./bashrc on any computer that we want to use these aliases on. Simply add the line

source ~/Dropbox/eyeP/ssh-aliases

and after reloading the profile ($ bash), you should be able to use the aliases. For now this script simply sets these aliases by the computers host-name which can be checked by running $ hostname. Obviously this may cause conflicts if you have the same host-name on two computers.