Remote Debugging

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Revision as of 12:33, 22 October 2012 by Chronos (talk | contribs) (note)


Remote debugging means you work on your local computer and you want to start and debug a program on another computer, the remote machine. In the following examples the name of the local computer is 'localcomp' and the name of the remote computer is 'remotecomp'.


Note: The "GNU Debugger through SSH" has some limitations. Also the implementation is still experimental, and does not prevent the use of unimplemented/limited features. (Trying to do any of the following, may lead to the debugger entering an error state)

  • It is currently not possible to use the "Pause" function to interrupt the running application.
  • It is not possible to modify break-/watch-points, while the application in the debugger is running.
  • One should no switch editor tabs, or open/close units, while the application in the debugger is running.
The 2nd and 3rd can be done, if the app in the debugger is paused. The only way for the app to become paused is by reaching a breakpoint that was set before the app was run.

Using SSH (Secure Shell)

SSH (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine. It is intended to replace rlogin and rsh, and provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP/IP ports can also be forwarded over the secure channel.

See the SSH man page for details. This text only handles ssh protocol 2. For differences for protocol 1 see the SSH man page.

Requirements for Lazarus

You must be able to log in via ssh to the remote machine (the computer where the program will run). This means the remote machine has an installed and running ssh server and you have an account allowed to login from your local machine (the computer where the lazarus IDE is running).

You can test this by doing:

[]$ ssh username@remotecomp ls -la

This will create a ssh connection to 'remotecomp' with the username 'username' and after authentification it will print out a directory listing and return.

Configuring SSH

The IDE needs a ssh connection without prompting for a password. There are a lot of possibilities to achieve this. This text only describes a few. For security reasons it is strongly recommended that you read the SSH manpage.

Solution 1: User based authentification.

This will allow one specific user on the local computer to establish a ssh connection to the remote computer as a specific user without prompting for password.

ToDo: describe the server settings. On redhat this works without any change.
Step 1
create the rsa key on the local machine

This will create two files on the local machine:

 ~/.ssh/id_rsa and ~/.ssh/

If you already have these files, skip this step.

 []$ ssh-keygen -t rsa

Keep the default and leave the passphrase empty.

Step 2
copy the public rsa key of the local machine to the remote machine
[]$ scp ~/.ssh/     
Step 3
create on the remote machine the file ~/.ssh/authorized_keys2
[]$ ssh user@remotecomp
[]$ touch ~/.ssh/authorized_keys2
[]$ chmod 600 ~/.ssh/authorized_keys2

The chmod will set the permissions to only allow yourself to read the file. ssh wants this.

 []$ cat >> ~/.ssh/authorized_keys2
 []$ rm
 []$ exit
Step 4

You should now be able to login without password.

 []$ ssh user@remotecomp
Step 5
Setup the ssh debugger in the IDE