Persistent PuTTY sessions for multiple windows

gnu-screenpersistentputtyssh

I'm working in various Linux environments through PuTTY connections which break from time to time. I'm looking for a solution to make the PuTTY windows persist (e.g. if I was editing a file, then after reconnecting I should be in the same editor with the same file open at the same place), with the following requirements:

it shouldn't require any manual setup at the beginning of the session or after reconnection (I don't want to type in screen or anything like that)
I have several windows open to the same machine with the same user, which tend to disconnect at the same time
the number/role of windows is not constant (it's not like I have an mc window, a mysql window and a "script runner" window; sometimes I use one window for search or for SVN commands, other times I need several at the same time)
sometimes I need to change the properties of the windows for a task (large window for grepping/editing, small windows because I need to see two of them at the same time, red background because I am modifying the live database in MySQL etc), so I need to get the same console back in the same window after a reconnect

Is there a way to achieve this? I suppose I should use screen or something equivalent, but how does it know which window I am reconnecting from? Is there some way to pass a unique window identifier to the shell from PuTTY?

Best Answer

The quick and clean solution

Edit your ~/.bashrc to run screen -r. Then you will be reattached to a running screen session automatically when you log in.

The fulfilling solution

Create a user for each screen session (Windows-window/PuTTY session) you intend to have open as a maximum.
Connect to the server using each of the newly created users and run "screen -S username" to start a session named with their username.
Append "screen -r $(whoami)" to each user's ~/.bashrc
Save a putty session for each of the users on your desktop or in PuTTY to add them to your superbar's jumplist or wherever you want your shortcuts, and use them to start up each session. This will also enable you to

EDIT: I would preferrably focus on fixing the timeout issue. It's a security feature, I know, but it shouldn't disconnect you while you are sending input.

Windows XP or prior Operating system only:

I wrote this answer 9 years ago for Windows XP, Putty software is 21 years old and so this answer is useful for historical purposes. Window's current smartphone-based Zune-OS for Desktop has broken Putty at the network level, in pursuit of irritating away all points of entry or exit that are not part of the pay-for-play Azure Vendor tool stack.

Putty has a feature which attempts to fix this problem:

Network Error: Software caused connection abort

Start Putty
Load your connection settings if you have them saved
Click on “Connection”
On the section that says "Sending of null packets to keep session active", Changed it to 5 seconds. 300 seconds may be better if network outages are your problem, read below for details.

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How keepalives to prevent disconnection with Putty:

Some network routers and firewalls need to keep track of all connections through them. Usually, these firewalls will assume a connection is dead if no data is transferred in either direction after a certain time interval. This can cause PuTTY sessions to be unexpectedly closed by the firewall if no traffic is seen in the session for some time.

The keepalive option (‘Seconds between keepalives’) allows you to configure PuTTY to send data through the session at regular intervals, in a way that does not disrupt the actual terminal session. If you find your firewall is cutting idle connections off, you can try entering a non-zero value in this field. The value is measured in seconds; so, for example, if your firewall cuts connections off after ten minutes then you might want to enter 300 seconds (5 minutes) in the box.

Reduce the problem using putty autologin and "screen" tool

Putty cannot handle a crappy wifi that loses connectivity for minutes at a time. A work around is to use autologin and screen.

It is a non trivial problem for putty to re synchronize your terminal after a minute long loss in internet connection. You run risks of man in the middle attacks during an outage. You would have to re-authenticate yourself anyway to make sure. Putty doesn't impose that on you, it just drops you.

So use autologin so putty can auto login on your behalf.

Generate a private key with the puttygen tool on the computer you are putty with.
Paste the public key in your /home/youruser/.ssh/authorized_keys on the server side, on the server that you are using putty go login to.
Make the private key accessible to putty in the putty settings Connection->SSH->Auth
Add the private key by specifying the private key file under: "Private key file for authentication".
Save the putty connection settings.

Then you would be able to double click your connection through putty, and it should take you right in to the terminal without typing username/password.

So now you can hook a login to putty on that connection with a keyboard combination like F6. So when the wifi goes bad and you get dropped. You mash down F6 and you're back logged in.

BUT you still lose the state of your terminal! How to fix that? Use the "screen" program. Make a new screen by typing 'screen'. A new screen is created.

When you get kicked out and auto login, you can reattach to your screen. Here is a tutorial on how to do that: http://www.tecmint.com/screen-command-examples-to-manage-linux-terminals/

It's a hassle to type in screen and reconnect every time you get dropped. So you can write a script that will "auto bring you back to the last available screen" to make it transparent.

So then when the putty terminal freezes. It looks like this: You make a snort of contempt, mash down Alt+F4 to close putty, Mash down F6. And in 6 seconds you are back right where you left off.

Even better solution, in theory

In theory you could script out this entire above process, so the terminal detects when it has been dropped, and does all the above steps for you on restoration of the internet connection. If anyone knows a program that does this automatically let me know. It would be neat.

Sources:

http://the.earth.li/~sgtatham/putty/0.58/htmldoc/Chapter4.html#config-keepalive

http://rafaelwolf.com/?p=516