Manual Reference Pages  - avc_context_to_sid (3)


avc_context_to_sid, avc_sid_to_context, sidput, sidget, avc_get_initial_sid - obtain and manipulate SELinux security ID’s.



#include <selinux/selinux.h>

#include <selinux/avc.h>

int avc_context_to_sid(security_context_t ctx, security_id_t *sid);

int avc_sid_to_context(security_id_t sid, security_context_t *ctx);

int sidget(security_id_t sid);

int sidput(security_id_t sid);

int avc_get_initial_sid(const char *name, security_id_t *sid);


Security ID’s (SID’s) are reference-counted, opaque representations of security contexts.

avc_context_to_sid returns a SID for the given context in the memory referenced by sid, incrementing its reference count by 1.

avc_sid_to_context returns a copy of the context represented by sid in the memory referenced by ctx. The user must free the copy with freecon(3).

sidget increments the reference count of sid by 1.

sidput decrements the reference count of sid by 1. If the count ever reaches zero, the SID becomes invalid and must not be used any further.

avc_get_initial_sid returns a SID for the kernel initial security identifier specified by name


sidget and sidput return the new reference count. A return value of zero indicates an invalid SID.

avc_context_to_sid and avc_sid_to_context return zero on success. On error, -1 is returned and errno is set appropriately.


EINVAL The provided sid has a zero reference count and is invalid.
ENOMEM An attempt to allocate memory failed.


The expected usage pattern for these functions is that avc_context_to_sid will be called once to obtain a SID for a newly created object, sidget will be called on a SID when its object is duplicated, and sidput will be called on a SID when its object is destroyed. Proper reference counting is necessary to ensure that SID’s and associated cache entries are reclaimed from memory when no longer needed.


Eamon Walsh <>


avc_init(3), avc_has_perm(3), avc_cache_stats(3), avc_add_callback(3), getcon(3), freecon(3) selinux(8)

avc_context_to_sid (3) 27 May 2004
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