cap_clear(3) — Linux manual page


CAP_CLEAR(3)            Linux Programmer's Manual           CAP_CLEAR(3)

NAME         top

       cap_clear, cap_clear_flag, cap_get_flag, cap_set_flag,
       cap_fill_flag, cap_fill, cap_compare, cap_max_bits - capability
       data object manipulation

SYNOPSIS         top

       #include <sys/capability.h>

       int cap_clear(cap_t cap_p);
       int cap_clear_flag(cap_t cap_p, cap_flag_t flag);
       int cap_get_flag(cap_t cap_p, cap_value_t cap,
                        cap_flag_t flag, cap_flag_value_t *value_p);
       int cap_set_flag(cap_t cap_p, cap_flag_t flag, int ncap,
                        const cap_value_t *caps, cap_flag_value_t value);
       int cap_fill_flag(cap_t cap_p, cap_flag_t to,
                         const cap_t ref, cap_flag_t from);
       int cap_fill(cap_t cap_p, cap_flag_t to, cap_flag_t from);
       int cap_compare(cap_t cap_a, cap_t cap_b);
       cap_value_t cap_max_bits();

       Link with -lcap.

DESCRIPTION         top

       These functions work on a capability state held in working
       storage.  A cap_t holds information about the capabilities in
       each of the three flags, Permitted, Inheritable, and Effective.
       Each capability in a set may be clear (disabled, 0) or set
       (enabled, 1).

       These functions work with the following data types:

              identifies a capability, such as CAP_CHOWN.

              identifies one of the three flags associated with a
              capability (i.e., it identifies one of the three
              capability dimensions).  Valid values for this type are

              identifies the setting of a particular capability flag
              (i.e, the value of a capability in a set).  Valid values
              for this type are CAP_CLEAR (0) or CAP_SET (1).

       cap_clear() initializes the capability state in working storage
       identified by cap_p so that all capability flags are cleared.

       cap_clear_flag() clears all of the capabilities of the specified
       capability flag, flag.

       cap_get_flag() obtains the current value of the capability flag,
       flag, of the capability, cap, from the capability state
       identified by cap_p and places it in the location pointed to by

       cap_set_flag() sets the flag, flag, of each capability in the
       array caps in the capability state identified by cap_p to value.
       The argument, ncap, is used to specify the number of capabilities
       in the array, caps.

       cap_fill_flag() fills the to flag of one capability set, with the
       values in the from flag of a reference capability set.

       cap_fill() fills the to flag values by copying all of the from
       flag values.

       cap_compare() compares two full capability sets and, in the
       spirit of memcmp(), returns zero if the two capability sets are
       identical. A positive return value indicates there is a
       difference between them. The returned value carries further
       information about the cap_flag_t flag differences. Specifically,
       the macro CAP_DIFFERS (value, flag) evaluates to non-zero if the
       returned value differs in its flag components.

       cap_max_bits() returns the number of capability values known to
       the running kernel. This may differ from libcap's list known at
       compilation time. Unnamed, at compilation time, capabilites can
       be referred to numerically and libcap will handle them
       appropriately. Note, the running kernel wins and it gets to
       define what "all" capabilities means.

RETURN VALUE         top

       cap_clear(), cap_clear_flag(), cap_get_flag() cap_set_flag() and
       cap_compare() return zero on success, and -1 on failure. Other
       return values for cap_compare() are described above. The function
       cap_max_bits() returns a numeric value of type cap_value_t that
       is one larger than the largest actual value known to the running

       On failure, errno is set to EINVAL, indicating that one of the
       arguments is invalid.

CONFORMING TO         top

       These functions are mostly as per specified in the withdrawn
       POSIX.1e draft specification.  The following are Linux
       extensions: cap_fill(), cap_fill_flag(), cap_clear_flag(),
       cap_compare() and cap_max_bits().

SEE ALSO         top

       libcap(3), cap_copy_ext(3), cap_from_text(3), cap_get_file(3),
       cap_get_proc(3), cap_init(3), capabilities(7)

COLOPHON         top

       This page is part of the libcap (capabilities commands and
       library) project.  Information about the project can be found at
       ⟨⟩.  If you
       have a bug report for this manual page, send it to (please put "libcap" in the Subject line).
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-06-24.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

                               2022-10-16                   CAP_CLEAR(3)

Pages that refer to this page: cap_copy_ext(3)cap_from_text(3)cap_get_file(3)cap_get_proc(3)cap_init(3)libcap(3)capabilities(7)