Configuring UDB

This section lists each of UDB’s configuration parameters, together with a description, or a link to a description.

Parameters can be configured in three ways:

  1. Using Configuration commands in Initialization files.

  2. Passing command-line options to udb.

  3. Setting environment variables with names starting UNDO_.

Autorun mode

After attaching to or launching a program, continue the program automatically.

By default, UDB stops the program after attaching or launching.

Set this using the --autorun command-line option, or set UNDO_autorun=true in the environment.

Batch mode

UDB does not take input from the user, and exits as soon as it has processed all the --command and --eval-command options. Implies Quiet startup.

Set this using the --batch command-line option. or set UNDO_batch=true in the environment.

Checking for updates

Whether UDB checks for a newer release at start-up.

auto (the default) checks if it is a day or more since the last check; yes always checks; no and never don’t check.

If auto or never, the setting becomes the new default.

Set this using the --checkupdates command-line option or the UNDO_checkupdates environment variable.

Deferring recording

See Starting UDB with recording disabled.

Quiet startup

Don’t print version number and licensing information on startup.

Set this using the --quiet command-line option, or set UNDO_quiet=true in the environment.

Event log mode

See Using a straight event log.

Instrumentation heap size

The size of the just-in-time translation cache, as a number followed by an optional multiplier (K for kilobytes, M for megabytes, or G for gigabytes), or 0 to choose a suitable size.

The Undo Engine uses just-in-time compilation in order to record the execution history of the program being debugged, and maintains a cache of translated code. The minimum size for the cache is 32M, which will allow approximately 3.2MB of x86 native code to be translated. Programs with a very large working set of instructions may benefit from a larger value.

Set this using the --instr-heapsize command-line option or the UNDO_instrheapsize environment variable.

Maximum event log size

See Configuring event log size.

Memory pressure threshold

See Snapshots adaptation.

Replay standard streams

Replay writes to standard output and standard error.

Side effects are normally suppressed in replay, but for orientation when debugging it can be helpful to replay writes to the standard streams.

Turn this off by setting UNDO_replay_standard_streams=false in the environment.

Maximum number of snapshots

See Configuring snapshots.

Temporary directory root

Directory used by UDB for its temporary files.

By default, UDB uses one of the directories specified by the Temporary directory roots configuration parameter.

Set this using the --tmpdir-root command-line option, or the UNDO_tmpdir_root environment variable.

Temporary directory roots

Semicolon-separated list of directories where temporary files can be placed.

By default, temporary files are placed in /tmp or /var/tmp.

Set this using the UNDO_tmpdir_roots environment variable.


See Timezones.