CAPNG_SET_ROOTID(3) Libcap-ng API CAPNG_SET_ROOTID(3)

capng_set_rootid - set namespace root id

#include <cap-ng.h>

int capng_set_rootid(uid_t rootid);

capng_set_rootid sets the root user ID for file capabilities operations. The value is host-endian and relative to the caller's user namespace. Pass CAPNG_UNSET_ROOTID to clear a previously selected namespace root ID and go back to writing regular V2 file capabilities. Other values select V3 file capabilities; the kernel validates and maps the user ID when the capabilities are written.

On success, it returns 0. It returns -1 if there is an internal error or the kernel headers used to build the library do not support V3 file capabilities.

capng_apply_caps_fd(3), capabilities(7)

Steve Grubb

March 2026 Red Hat