GSoC Commons-Net SSH Concluded

Today is officially “pencils-down” day for the Google Summer of Code Project 2009. I have been a mentor this year for the Apache Commons-Net SSH project, which aims to add SSH and SCP support to Commons-Net.

The project has been a great success, mainly down to the super work performed by the student, Shikhar, who has put in tremendous work to get a fully functional SSH/SCP client built (with thanks to the efforts of the Mina SSHD project, whose codebase we originally based the effort on). All of the goals for the project have been ticked, and some extra ones accomplished too.

I had great help and input from Chico, another Apache committer, throughout the project, and so it’s been a great experience all round. This will form the basis of a release, but for now, the code is hosted on googlecode at: http://code.google.com/p/commons-net-ssh/

Headless R / X11 and Cygwin/X

Running R on a Linux server in headless mode (i.e. producing graphics without XWindows running) can be tricky. Some people recommend using a virtual X framebuffer. However, I’ve found that the best approach (at least im my opinion) is to use the R interface to Cairo. This allows R to produce png graphics in headless mode, and also produces very nice looking graphs. I configured R as follows (after downloading and building pixman-0.15.18, and cairo-1.8.8:

./configure --with-gnu-ld --with-x --with-cairo

This will produce an R binary with cairo support that can be run non-interactively and produce graphical output – very useful for running automated statistical reports.

You can check that Cairo support is enabled by checking the return value of the capabilities() function:

> capabilities()
jpeg png tiff tcltk X11 aqua http/ftp sockets
TRUE TRUE FALSE FALSE FALSE FALSE TRUE TRUE
libxml fifo cledit iconv NLS profmem cairo
TRUE TRUE TRUE TRUE TRUE FALSE TRUE

Finally, some notes on connecting X11 clients using Cygwin (which I always forget how to do). On the server, check /etc/ssh/sshd_config for the line

X11Forwarding yes

And then run a local X server:

XWin -clipboard -emulate3buttons -multiwindow

Once this is running, from an xterm, run ssh, passing in the -X argument to enable X forwarding.

ssh -X -l username myserver

X11-based applications can then be run from this session.