An R installation can have up to three types of library paths available to the user:
The user library, where R packages downloaded and installed by the current user are installed. This library path is only visible to that specific user.
The site library, where R packages maintained by administrators of a system are installed. This library path, if it exists, is visible to all users on the system.
The default library, where R packages distributed with R itself are installed. This library path is visible to all users on the system.
Normally, only so-called "base" and "recommended" packages should be installed
in the default library. (You can get a list of these packages with
installed.packages(priority = c("base", "recommended"))). However, it is
possible for users and administrators to install packages into the default
library, if the filesystem permissions permit them to do so. (This, for
example, is the default behavior on macOS.)
Because the site and default libraries are visible to all users, having those accessible in renv projects can potentially break isolation -- that is, if a package were updated in the default library, that update would be visible to all R projects on the system.
To help defend against this, renv uses something called the "sandbox" to isolate renv projects from non-"base" packages that are installed into the default library. When an renv project is loaded, renv will:
Create a new, empty library path (called the "sandbox"),
Link only the "base" and "recommended" packages from the default library into the sandbox,
Mark the sandbox as read-only, so that users are unable to install packages into this library,
Instruct the R session to use the "sandbox" as the default library.
This process is mostly transparent to the user. However, because the sandbox
is read-only, if you later need to remove the sandbox, you'll need to reset
file permissions manually; for example, with renv::sandbox$unlock().
If you'd prefer to keep the sandbox unlocked, you can also set:
in an appropriate startup .Renviron or Renviron.site file.
The sandbox can also be disabled entirely with:
The sandbox library path can also be configured using the RENV_PATHS_SANDBOX
environment variable: see paths for more details.