Using the LiveRecorder tool

Depending on your license, LiveRecorder can be provided as a command-line tool called live-record that allows you to record the execution of a process on your Linux command line. This tool can be used a bit like the strace tool on Linux, except that it makes LiveRecorder recordings instead of printing system calls and signals.

The tool will be installed to your preferred location when you run make install, and usage notes are printed if you run live-record with the --help option.

Usage example

The LiveRecorder tool can be used both to launch a new process and to attach to an existing one.

You can launch a program with the path path/to/program with program arguments arg1, arg2 and arg3, with the following command:

$> live-record path/to/program arg1 arg2 arg3

When your application terminates, live-record will write a recording to a file whose name is printed to your terminal. If you wish to specify a recording filename, use the --recording-file option as follows:

$> live-record --recording-file my_recording.undo path/to/program arg1 arg2 arg3

Ordinarily recordings are always written when your application terminates. You can use the --save-on option to fine-tune the circumstances under which the tool saves a recording. For example, if you want a recording to be saved only if the application terminates abnormally in some way, either due to being terminated by a signal or returning a non-zero exit status, use the error value for the --save-on option:

$> live-record --save-on error --recording-file my_recording.undo path/to/program arg1 arg2 arg3

Alternatively, if you only want a recording file if your application terminates due to a signal, use the signal value for the --save-on option.

You can attach to an already running process by using the --pid option. For example, to attach to process 1234:

$> live-record --pid 1234

All options apply to both the launch and attach cases.

Options

-h, --help

Show help summary.

-v, --version

Print version information and then exit.

-q, --quiet

Suppress output from the tool on standard streams, unless an error occurs.

-p PID, --pid PID

Attach to the process PID and start recording it.

-o FILENAME, --recording-file FILENAME

Save the LiveRecorder recording to FILENAME.

--recording-dir DIRNAME

Save the LiveRecorder recording in the directory DIRNAME. This is ignored if the -o or --recording-file option is given.

--save-on CIRCUMSTANCE[,CIRCUMSTANCE,...]

Save only in the given circumstances, which must be one or more of:

always	Always save a recording. This is the default behaviour if the --save-on option is not given.
detach	Save when live-record detaches from the program due to receiving SIGUSR1 or SIGINT.
error	Shorthand for failure,signal,unsupported.
failure	Save when the program exits with a non-zero status.
signal	Save when the program exits due to an unhandled signal.
success	Save when the program exits with a zero status.
unsupported	Save when the program does something that is not supported by live-record.

--max-event-log-size SIZE[K|M|G]

Set the maximum event log size.

--thread-fuzzing

Enable Thread Fuzzing, which varies the scheduling of threads to attempt to provoke race conditions.

--tmpdir-root DIRNAME

Set the directory used by live-record for its temporary files.

Signals

live-record has special handling for the following signals, if they are delivered to the LiveRecorder controller process:

SIGINT

In the attach case, this signal causes live-record to detach from the target process, saving a recording if the --save-on option includes detach. In the launch case, this signal is delivered to the target process, and if it causes the target process to exit then live-record saves a recording if the --save-on option includes signal.

SIGUSR1

live-record detaches from the target process, saving a recording if the --save-on option includes detach.

SIGHUP

This signal is delivered to the target process, and if it causes the target process to exit then live-record saves a recording if the --save-on option includes signal.

SIGTERM

live-record exits cleanly without saving a recording, in both the attach and launch cases. The --save-on option is ignored.

In the attach case, the LiveRecorder controller process is the instance of live-record, but in the launch case it is a daemon process that can be found by its name undo-lr-PID, where PID is the id of the target process, for example, by using pgrep.

Warning

The SIGSTOP signal is used internally by LiveRecorder and cannot be reliably delivered to the target process. If you need to temporarily stop the target process while it is being recorded you can instead use the SIGTSTP signal.

Notes

• As with tools like strace (but unlike GDB), the path to the executable you wish to record must either be on your PATH, or must be fully qualified.

• In the launch case, live-record forks a daemon process to do the recording, and execs the target process. This means that the target process is a direct child of the shell which ran live-record.

• The exit code of live-record is the exit code of the recorded program, unless live-record detaches on a signal as described above.

• Your customer UID will be embedded in each recording created by live-record, and these recordings will only be loadable by a correspondingly licensed udb.

Limitations

The limitations of all tools built around the Undo Engine apply also to the live-record tool. See System requirements for details. The following limitations apply to live-record only:

• live-record does not always report errors very well. If live-record fails and does not appear to produce any useful output, please contact us at support@undo.io.