Packages can be installed globally (i.e., for all users of the system) or locally (i.e., for the current user only).
Global packages are installed by default in a system-wide location. This is usually a subdirectory of the folder where Octave itself is installed. Therefore, Octave needs write access to this folder to install global packages, which is usually only available when Octave is run with administrative privileges, such as when run as root (or superuser) on Unix-like systems, or run with elevated privileges ("Run as administrator") on Windows.
In contrast, local packages are installed by default in the user’s home directory (or user profile on Windows) and are only available to that specific user. Usually, they can be installed without administrative privileges.
When Octave is running with administrative privileges, pkg will install
packages to the global package location by default. Otherwise, packages will
be installed to the local location by default. The user can override this
default installation location with optional arguments (-local or
-global) as described below. The currently used default package
installation location can be queried with pkg prefix.
For global and local packages, there are separate databases holding the information about the installed packages. If some package is installed globally as well as locally, the local installation takes precedence over ("shadows") the global one. Which (global or local) package installation is used can also be manipulated by using prefixes and/or using the ‘local_list’ input argument. Using these mechanisms, several different releases of the same package can be installed side by side as well (but cannot be loaded simultaneously).
Packages might depend on external software and/or other packages. To be able to install such packages, these dependencies should be installed beforehand. A package that depends on other package(s) can still be installed using the -nodeps flag. The effects of unsatisfied dependencies on external software—like libraries—depends on the individual package.
Packages must be loaded before they can be used. When loading a package, Octave performs the following tasks:
pkg load is called without
the -nodeps option), the package is not loaded immediately. Instead,
those dependencies are loaded first (recursively if needed).
This load order leads to functions that are provided by dependencies being potentially shadowed by functions of the same name that are provided by top-level packages.
Each time, a package is added to the search path, initialization script(s) for the package are automatically executed if they are provided by the package.