Capsicum(4) lightweight OS capability and sandbox framework




is a lightweight OS capability and sandbox framework implementing a hybrid capability system model. can be used for application and library compartmentalisation, the decomposition of larger bodies of software into isolated (sandboxed) components in order to implement security policies and limit the impact of software vulnerabilities.

provides two core kernel primitives:

capability mode
A process mode, entered by invoking cap_enter2, in which access to global OS namespaces (such as the file system and PID namespaces) is restricted; only explicitly delegated rights, referenced by memory mappings or file descriptors, may be used. Once set, the flag is inherited by future children processes, and may not be cleared.
Limit operations that can be called on file descriptors. For example, a file descriptor returned by open(2) may be refined using cap_rights_limit2 so that only read(2) and write(2) can be called, but not fchmod(2). The complete list of the capability rights can be found in the rights(4) manual page.

In some cases, requires use of alternatives to traditional POSIX APIs in order to name objects using capabilities rather than global namespaces:

process descriptors
File descriptors representing processes, allowing parent processes to manage child processes without requiring access to the PID namespace; described in greater detail in procdesc(4).
anonymous shared memory
An extension to the POSIX shared memory API to support anonymous swap objects associated with file descriptors; described in greater detail in shm_open2.


first appeared in Fx 9.0 , and was developed at the University of Cambridge.


was developed by An -nosplit An Robert Watson Aq [email protected] and An Jonathan Anderson Aq [email protected] at the University of Cambridge, and An Ben Laurie Aq [email protected] and An Kris Kennaway Aq [email protected] at Google, Inc., and An Pawel Jakub Dawidek Aq [email protected] .


is considered experimental in Fx .