Working directly on your server? How to backup and sync your dev environment with unison

I have a server running freebsd since some time now, and was wondering about the possibility to directly have a development environment ready to use when I get a internet connexion, even if I’m not on my computer.

Since I use vim to code, and spend most of my time in a console while developing, it’s possible to work via ssh, from everywhere.

The only problem is the synchronisation of the source code, config files etc. from my machine to the server.

Unison provides an interesting way to synchronise two folders, even over a network. So let’s do it !

Creating the jail

In case you don’t use FreeBSD, you can skip this section.

# I have a flavour jail named default
$ ezjail-admin -f default
$ ezjail-admin start

In my case, because the “default” flavour contains already a lot of interesting things, my jail come already setup with ssh, bash and vim for instance, but maybe you’ll need it in your case.

I want to be redirected to the ssh of the jail when I connect to the host with the 20006 port. Add lines in /etc/pf.conf:

    rdr on $ext_if proto tcp from any to $ext_ip port 20006 -> $workspace_jail port 22

Reload packet filter rules

$ /etc/rc.d/pf reload

Working with unison

Now that we’ve set up the jail. Set up unison on the server and on your client. Unison is available on the freebsd ports so just install it

$ ssh -p 20006
$ make -C /usr/ports/net/unison-nox11 config-recursive
$ make -C /usr/ports/net/unison-nox11 package-recursive

Install as well unison on your local machine. Double check to install the same version on the client and on the server. Ubuntu contains the 2.27.57 as well as the 2.32.52.

Check that unison is installed and reachable via ssh from your machine

$ ssh -p 20006 unison -version
unison version 2.27.157
$ unison -version
unison version 2.27.57

Let sync our folders

The first thing I want to sync is my vim configuration. Well, it’s already in a git repository but let’s try to use unison for it right now.

I have two machines then: workspace, the jail, and ecureuil my laptop.

unison .vim ssh://
unison .vimrc ssh://

It is also possible to put all the informations in a config file, and then to only run unison. (fire up vim \~/.unison/default.prf.

Here is my config:

    root = /home/alexis
    root = ssh://

    path = .vimrc
    path = dotfiles
    path = dev

    follow = Name *

My vimrc is in fact a symbolic link on my laptop, but I don’t want to specify each of the links to unison. That’s why the follow = Name * is for.

The folders you want to synchronize are maybe a bit large. If so, considering others options such as rsync for the first import may be a good idea (I enjoyed my university huge upload bandwith to upload 2GB in 20mn ;)

Run the script frequently

Once that done, you just need to run the unison command line some times when you want to sync your two machines. I’ve wrote a tiny script to get some feedback from the sync:

import os
from datetime import datetime

DEFAULT_LOGFILE = "~/unison.log"
PROGRAM_NAME = "Unison syncer"

def sync(logfile=DEFAULT_LOGFILE, program_name=PROGRAM_NAME):
    # init
    display_message = True
    error = False

    before =
    # call unison to make the sync
    os.system('unison -batch > {0}'.format(logfile))

    # get the duration of the operation
    td = - before
    delta = (td.microseconds + (td.seconds + td.days * 24 * 3600) * 10**6) / 10**6

    # check what was the last entry in the log
    log = open(os.path.expanduser(logfile))
    lines = log.readlines()
    if 'No updates to propagate' in lines[-1]:
        display_message = False
        output = [l for l in lines if "Synchronization" in l]

        message = output[-1]
        message += " It took {0}s.".format(delta)

    if display_message:
        os.system('notify-send -i {2} "{0}" "{1}"'.format(program_name, message,
            'error' if error else 'info'))

if __name__ == "__main__":

This is probably perfectible, but that does the job.

Last step is to tell you machine to run that frequently. That’s what crontab is made for, so let’s crontab -e:

    $ * */3 * * * . ~/.Xdbus; /usr/bin/python /home/alexis/dev/python/unison-syncer/

The \~/.Xdbus allows cron to communicate with your X11 session. Here is its content.


# Get the pid of nautilus
nautilus_pid=$(pgrep -u $LOGNAME -n nautilus)

# If nautilus isn't running, just exit silently
if [ -z "$nautilus_pid" ]; then
exit 0

# Grab the DBUS_SESSION_BUS_ADDRESS variable from nautilus's environment
eval $(tr '\0' '\n' < /proc/$nautilus_pid/environ | grep '^DBUS_SESSION_BUS_ADDRESS=')

# Check that we actually found it
if [ -z "$DBUS_SESSION_BUS_ADDRESS" ]; then
echo "Failed to find bus address" >&2
exit 1

# export it so that child processes will inherit it

And it comes from here.

A sync takes about 20s + the upload time on my machine, which stay acceptable for all of my developments.