Below are the R options and environment variables that are used by the parallelly package and packages enhancing it.

WARNING: Note that the names and the default values of these options may change in future versions of the package. Please use with care until further notice.

Backward compatibility with the future package

The functions in the parallelly package originates from the future package. Because they are widely used within the future ecosystem, we need to keep them backward compatible for quite a long time, in order for all existing packages and R scripts to have time to adjust. This also goes for the R options and the environment variables used to configure these functions. All options and environment variables used here have prefixes parallelly. and R_PARALLELLY_, respectively. Because of the backward compatibility with the future package, the same settings can also be controlled by options and environment variables with prefixes future. and R_FUTURE_ until further notice, e.g. setting option future.availableCores.fallback=1 is the same as setting option parallelly.availableCores.fallback=1, and setting environment variable R_FUTURE_AVAILABLECORES_FALLBACK=1 is the same as setting R_PARALLELLY_AVAILABLECORES_FALLBACK=1.

Configuring number of parallel workers

The below R options and environment variables control the default results of availableCores() and availableWorkers().


(logical) The default value of argument logical as used by availableCores(), availableWorkers(), and availableCores() for querying parallel::detectCores(logical = logical). The default is TRUE just like it is for parallel::detectCores().


(character vector) Default lookup methods for availableCores(). (Default: c("system", "nproc", "mc.cores", "_R_CHECK_LIMIT_CORES_", "PBS", "SGE", "Slurm", "LSF", "fallback", "custom"))


(function) If set and a function, then this function will be called (without arguments) by availableCores() where its value, coerced to an integer, is interpreted as a number of cores.


(integer) Number of cores to use when no core-specifying settings are detected other than "system" and "nproc". This options makes it possible to set the default number of cores returned by availableCores() / availableWorkers() yet allow users and schedulers to override it. In multi-tenant environment, such as HPC clusters, it is useful to set environment variable R_PARALLELLY_AVAILABLECORES_FALLBACK to 1, which will set this option when the package is loaded.


(integer) Number of "system" cores used instead of what is reported by availableCores(which = "system"). This option allows you to effectively override what parallel::detectCores() reports the system has.


(integer) The minimum number of cores availableCores() is allowed to return. This can be used to force multiple cores on a single-core environment. If this is limit is applied, the names of the returned value are appended with an asterisk (*). (Default: 1L)


(integer) Number of cores to set aside, i.e. not to include.


(character vector) Default lookup methods for availableWorkers(). (Default: c("mc.cores", "_R_CHECK_LIMIT_CORES_", "PBS", "SGE", "Slurm", "LSF", "custom", "system", "fallback"))


(function) If set and a function, then this function will be called (without arguments) by availableWorkers() where its value, coerced to a character vector, is interpreted as hostnames of available workers.

Configuring forked parallel processing

The below R options and environment variables control the default result of supportsMulticore().


(logical) Enable or disable forked processing. If FALSE, multicore futures becomes sequential futures. If NA, or not set (the default), the a set of best-practices rules decide whether should be supported or not.


(character) Controls whether a warning should be produced or not whenever multicore processing is automatically disabled because the environment in which R runs is considered unstable for forked processing, e.g. in the RStudio environment. If "warn" (default), then an informative warning is produces the first time 'multicore' or 'multiprocess' futures are used. If "quiet", no warning is produced.

Configuring setup of parallel PSOCK clusters

The below R options and environment variables control the default results of makeClusterPSOCK() and its helper function makeNodePSOCK() that creates the individual cluster nodes.


(character) If "parallel" (default), the PSOCK cluster nodes are set up concurrently. If "sequential", they are set up sequentially.


(logical) If TRUE (default), after the nodes have been created, they are all validated that they work by inquiring about their session information, which is saved in attribute session_info of each node.


(numeric) The maximum time (in seconds) allowed for each socket connection between the master and a worker to be established (defaults to 2*60 seconds = 2 minutes).


(numeric) The maximum time (in seconds) allowed to pass without the master and a worker communicate with each other (defaults to 302460*60 seconds = 30 days).


(logical) If FALSE (default), the communication between master and workers, which is binary, will use small-endian (faster), otherwise big-endian ("XDR"; slower).


(character string) If set to another value than "NULL", then option socketOptions is set to this value on the workers during startup. See base::socketConnection() for details. (defaults to "no-delay")


(character vector) The command to be run on the master to launch a process on another host.


(character vector) Addition command-line options appended to rshcmd. These arguments are only applied when connecting to non-localhost machines.


(integer) The maximum number of attempts done to launch each node. Only used when setting up cluster nodes using the sequential strategy.


(numeric) The number of seconds to wait before trying to launch a cluster node that failed to launch previously. Only used when setting up cluster nodes using the sequential strategy.

Options for debugging


(logical) If TRUE, extensive debug messages are generated. (Default: FALSE)

Environment variables that set R options

All of the above R parallelly.* options can be set by corresponding environment variables R_PARALLELLY_* when the parallelly package is loaded. For example, if R_PARALLELLY_MAKENODEPSOCK_SETUP_STRATEGY = "sequential", then option parallelly.makeNodePSOCK.setup_strategy is set to "sequential" (character). Similarly, if R_PARALLELLY_AVAILABLECORES_FALLBACK = "1", then option parallelly.availableCores.fallback is set to 1 (integer).

See also

To set R options when R starts (even before the parallelly package is loaded), see the Startup help page. The startup package provides a friendly mechanism for configuring R's startup process.


# Set an R option:
options(parallelly.availableCores.fallback = 1L)