Remote debugging

Remote debugging is used in situations where a program must be run on a different machine to where it is developed; in these cases it’s typically convenient to run the debugger on the development machine and have it control a program running on the test machine.

Installing udbserver on the target

udbserver is the component of UDB which tightly controls the program and enables it to be recorded and rewound. For those familiar with remote debugging via GDB, it is analogous to gdbserver. As such it must be installed on the target machine.

Installing can be as simple as copying the Undo release directory to the target machine, or making it available via a file-sharing mechanism such as NFS. Where storage space on the target is limited, the only required files are the version of udbserver appropriate to your target (see below) and the key file.

It is important that the date and time on the target device are set (approximately) correctly, otherwise udbserver will refuse to run.


The version of udbserver installed on the target must match the version of UDB used on the development machine.

Choosing the appropriate udbserver executable

Your LiveRecorder download contains a number of udbserver executables. The correct executable depends on the architecture for which the program was compiled, as follows:

OS Architecture udbserver executable
Linux Intel i386 udbserver_x32
Linux AMD/Intel x86-64 udbserver_x64
Linux ARMv8 AArch64 (enabled licenses only) udbserver_arm64


In previous versions of UDB, the remote debugging server was called undodb-server (and the executables were called undodb-server_<arch>, where arch is the program’s architecture). For compatibility, the old executable names are still available but are now symbolic links to the udbserver_<arch> executables.

Basic usage

Start udbserver, using the --connect-port 0 option to request it to choose a TCP/IP port to listen on.

$ udbserver_x64 --connect-port 0 examples/cache &
6.4.0 (build 332939358beac0569f4f07cc0c76d689b22be1d1+) udbserver
Listening on port 46431


The path to the program being debugged must also be the full path, not a relative path. For example ../my_program will not work, but /home/myuser/myprogram will.

Connect to the server in UDB using the target remote command, for example:

$ udb -q examples/cache
Reading symbols from examples/cache...
not running> target remote localhost:46431
Remote debugging using localhost:46431
Connection established
Connection established
not running> start
Temporary breakpoint 1 at 0x8b0: file cache.c, line 65.
Starting program: examples/cache

Temporary breakpoint 1, main () at cache.c:65
65          cache_init();

If the program is already running, use the --pid option, for example:

$ examples/deadlock & echo $!
$ udbserver_x64 --pid 25794 --connect-port 0 &
6.4.0 (build 332939358beac0569f4f07cc0c76d689b22be1d1+) udbserver
Listening on port 36731

Command-line options


Automatically start the program as soon as UDB has connected. For example:

$ udbserver_x64 --autostart --connect-port 0 examples/cache &
6.4.0 (build 332939358beac0569f4f07cc0c76d689b22be1d1+) udbserver
Listening on port 37247
$ udb -q examples/cache
Reading symbols from examples/cache...
not running> target remote localhost:37247
Remote debugging using localhost:37247
0x00007fdc8cf47090 in _start () from /lib64/
Connection established
Connection established


Autostart is required for remote debugging to work correctly from some IDEs, including CLion and Eclipse, and is implicit in the suggested command-line when launching for IDE remote debugging.

--connect-port PORT

Listen for new connections on PORT. Specify port 0 to choose an available port.


Start the program in deferred-recording mode.


Run as a daemon. That is, detach from the controlling terminal and run in the background.

--daemon-output FILENAME

If the --daemon option is given, redirect standard output and standard error to FILENAME.

--keyfile KEYFILE

Use the license key from KEYFILE. By default, use the file named key in the same directory as udbserver.

--load-file RECORDING

Load the LiveRecorder recording named by RECORDING.

--pid PID

Attach to the process with id PID.

--tmpdir-root DIRECTORY

The directory used by udbserver for its temporary files. See Temporary directory root.


Print version information and then exit.

Cross-architecture debugging

A common case in remote debugging is to have a developer machine running udb, connected over a network to a test machine running udbserver, and where the developer and test machines have different CPU architectures. In this case, use the set architecture command to tell udb the architecture of the program being debugged.

set architecture arch

Set the target architecture to arch. Supported architectures are:

OS Architecture Architecture
Linux Intel i386 i386
Linux AMD/Intel x86-64 i386:x86-64
Linux ARMv8 AArch64 (enabled licenses only) aarch64

show architecture

Show the target architecture.

IDE remote debugging

IDEs, including Eclipse and CLion, make certain assumptions about the behaviour of the remote debugging server. These assumptions are based on vanilla gdb’s behaviour. In order to match those expectations, the suggested command-line when launching the server for remote debugging within an IDE is:

udbserver_<arch> <port-number> <full-path-to-program>