Ubuntu Blog

Make Documentation Easier to Read February 4, 2006

Today’s tip rules them all, for it puts you in the driver’s seat.

Debian (and ergo Ubuntu) has some of the best documentation in the world. The best thing about the documentation is that it is on your machine, not on the internet. However not many realize this, and many a problem that can be solved just by reading the documentation remains unsolved, and many a user resorts to forums, mailing lists etc when the answer is right there on their own computer. I am guilty too, having realized the power of RTFM-ing before.

You can browse most of the html documentation on your system by
Clicking the System -> Help menu item on the desktop taskbar. Besides Manual Pages, and other Documentation, you will find lots of docs for the different applications.

But what if the tool/library you installed does not come with a GUI, or a menu entry? The documentation for all packages is installed in /usr/share/doc. You could use the terminal to change to that directory and then look around to find the directory containing documentation for the package. Or you could use today’s tip 🙂

To make documentation easier to access, set CDPATH as follows:
$export CDPATH=.:/usr/local:/usr/share/doc

To make the change permanent (across terminal sessions/restarts), add the line to your ~/.bashrc file.

Now, to find documentation for package-name
Type:
$cd package-name
and then you can do an $ls to see what documentation is on offer. You can then use your favourite editor/pager to read the documentation.

Often, if you have problems with a package, it is good to read the README.Debian file to see if there are any special notes explaining workarounds or expected problems.
$ pager README.Debian

If there is a file called index.html, you can read the html documentation using
$firefox index.html

There, now you are all set to go exploring and find out more about the packages installed on your system. I was literally overjoyed to find the “CDPATH” variable for bash which makes things so much easier.

Keeping SSH Sessions Alive February 3, 2006

Scott Merrill writes in to say:

I noticed recently that ssh connections from my Ubuntu laptop to my
Debian server would time out and disconnect if I left the connection
idle for a long-ish period of time. This really annoyed me, because my
Debian desktop does not exhibit this behavior when connecting to the server.

I added the following line to /etc/ssh/ssh_config :
ServerAliveInterval 5

That seems to have fixed the problem, and my laptop can now remain
connected, though idle, to my server. Maybe this will help someone
else, too.

What this does, essentially is every 5 seconds, the client sends a small keep-alive packet to the server to make it look like the ssh connection is being actively used. The reason for Scott’s timeout could be a NAT firewall that seeks to minimize the nember of active connections to reduce its memory footprint, or to improve performance for other clients. Most firewalls and networks let you keep your connections alive for as long as you wish, but some may act up, and that’s when you can use Scott’s trick.

Tip: Change 5 to 240 or 300, so that instead of every 5 seconds, the keep-alive signal is sent only once in 4 or 5 minutes 🙂

Sorry it took me so long to post this useful tip, Scott.

Make sudo/gksudo remember passwords January 25, 2006

I use sudo and gksudo quite often. Now, if you use sudo in a terminal window, then you only have to enter the password the first time. But what if you have more than one terminal window, and try to use a sudo command in all of them? You will be prompted for your password the first time you use sudo in each terminal window. The same applies for gksudo.

This makes sense for a computer that is acting as a server. If you are logged in from multiple locations, and you enter the password for sudo in your current location, all the other locations are still “safe” since the person using the other terminals will still have to enter the password to use sudo. But when it comes to desktop use, this behaviour can be an annoyance.

I hate being prompted again and again for the sudo password (and the graphical gksudo password). For me, on my laptop, I want the sudo password to be “shared” between the different terminal windows, and with gksudo. It would be nice if the timestamp on the password was “global” to all terminals, and all the “gksudo” menu entries.

I ensure this by changing the following line in /etc/sudoers:
Defaults !lecture,tty_tickets,!fqdn

to
Defaults !lecture,!tty_tickets,!fqdn

Here, tty_tickets refers to “terminal tickets”, and I just changed it from using one ticket per terminal, to a common ticket, globally.

Again, this is not recommended for server installs, but may make life a little easier for average Joe Desktop Users.