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LJM Startup Configs

If you need to change LJM's configs either globally or quickly, you can edit the ljm_startup_configs.json file.

Default Location

Windows Vista and later:


Windows XP (deprecated):

C:\Documents and Settings\All Users\Application Data\LabJack\LJM\ljm_startup_configs.json

Mac OS X and Linux:



  • Parsed before any other configs are set, so config values that are manually set using the programmatic config functions (such as LJM_WriteLibraryConfigS) with take precedence over the values in ljm_startup_configs.json.
  • Parsed during LJM startup, so processes that have already loaded LJM will not be altered by new changes to ljm_startup_configs.json.
  • ljm_startup_configs.json (and the containing folder) may be overwritten when LJM updates, so if you'd like to make changes to the configurations that are loaded when LJM starts, use ljm_startup_configs.json as a template to make a different file in a different directory that you control, then load that file using the LJM_LoadConfigurationFile function at the beginning of your program.

Default Values

Use the string "default" to load the default value for each config parameter. Otherwise, see the "type" for each config parameter for what kinds of values can be accepted. Please see LabJackM.h for more information about what each config parameter does.

Configs that are not included in ljm_startup_configs.json will be given the default value.


ljm_startup_configs.json is parsed by LJM case-insensitively. LJM ignores every key in the top-level JSON object except for LJM_CONFIG_VALUES, as well as ignoring every "description", "type", and "values" fields. Other fields in LJM_CONFIG_VALUES which are not recognized by LJM will generate errors/warnings. LJM will also ignore lines starting with "//".

Windows Paths

Windows file paths must escape \ characters with \. For example, the path:


Must be escaped as:


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