cap_from_text(3) — Linux manual page


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

NAME         top

       cap_from_text, cap_to_text, cap_to_name, cap_from_name -
       capability state textual representation translation

SYNOPSIS         top

       #include <sys/capability.h>

       cap_t cap_from_text(const char *buf_p);
       char *cap_to_text(cap_t caps, ssize_t *len_p);
       int cap_from_name(const char *name, cap_value_t *cap_p);
       char *cap_to_name(cap_value_t cap);

       Link with -lcap.

DESCRIPTION         top

       These functions translate a capability state between an internal
       representation and a textual one.  The internal representation is
       managed by the capability functions in working storage. The
       textual representation is a structured, human-readable string
       suitable for display.

       cap_from_text() allocates and initializes a capability state in
       working storage. It then sets the contents of this newly created
       capability state to the state represented by a human-readable,
       nul-terminated character string pointed to by buf_p.  It returns
       a pointer to the newly created capability state.  When the
       capability state in working storage is no longer required, the
       caller should free any releasable memory by calling cap_free()
       with cap_t as an argument.  The function returns an error if it
       cannot parse the contents of the string pointed to by buf_p or
       does not recognize any capability_name or flag character as
       valid.  The function also returns an error if any flag is both
       set and cleared within a single clause.

       cap_to_text() converts the capability state in working storage
       identified by caps into a nul-terminated human-readable string.
       This function allocates any memory necessary to contain the
       string, and returns a pointer to the string.  If the pointer
       len_p is not NULL, the function shall also return the full length
       of the string (not including the nul terminator) in the location
       pointed to by len_p.  The capability state in working storage,
       identified by caps, is completely represented in the character
       string.  When the capability state in working storage is no
       longer required, the caller should free any releasable memory by
       calling cap_free() with the returned string pointer as an

       cap_from_name() converts a text representation of a capability,
       such as "cap_chown", to its numerical representation
       (CAP_CHOWN=0), writing the decoded value into *cap_p.  If cap_p
       is NULL no result is written, but the return code of the function
       indicates whether or not the specified capability can be
       represented by the library.

       cap_to_name() converts a capability index value, cap, to a
       libcap-allocated textual string. This string should be
       deallocated with cap_free().


       A textual representation of capability sets consists of one or
       more whitespace-separated clauses.  Each clause specifies some
       operations on a capability set; the set starts out with all
       capabilities lowered, and the meaning of the string is the state
       of the capability set after all the clauses have been applied in

       Each clause consists of a list of comma-separated capability
       names (or the word `all'), followed by an action-list.  An
       action-list consists of a sequence of operator flag pairs.  Legal
       operators are: `=', '+', and `-'.  Legal flags are: `e', `i', and
       `p'.  These flags are case-sensitive and specify the Effective,
       Inheritable and Permitted sets respectively.

       In the capability name lists, all names are case-insensitive.
       The special name `all' specifies all capabilities; it is
       equivalent to a list naming every capability individually.

       Unnamed capabilities can also be specified by number. This
       feature ensures that libcap can support capabilities that were
       not allocated at the time libcap was compiled. However, generally
       upgrading libcap will add names for recently allocated

       The `=' operator indicates that the listed capabilities are first
       reset in all three capability sets.  The subsequent flags (which
       are optional when associated with this operator) indicate that
       the listed capabilities for the corresponding set are to be
       raised.  For example: "all=p" means lower every capability in the
       Effective and Inheritable sets but raise all of the Permitted
       capabilities; or, "cap_fowner=ep" means raise the Effective and
       Permitted override-file-ownership capability, while lowering this
       Inheritable capability.

       In the case that the leading operator is `=', and no list of
       capabilities is provided, the action-list is assumed to refer to
       `all' capabilities.  For example, the following three clauses are
       equivalent to each other (and indicate a completely empty
       capability set): "all="; "="; "cap_chown,<every-other-

       The operators, `+' and `-' both require an explicit preceding
       capability list and one or more explicit trailing flags.  The `+'
       operator will raise all of the listed capabilities in the flagged
       capability sets.  The `-' operator will lower all of the listed
       capabilities in the flagged capability sets.  For example:
       "all+p" will raise all of the Permitted capabilities and
       "cap_fowner-i" will lower the override-file-ownership in the
       Inheritable set.

       The action list can consist of multiple operator flag pairs; the
       actions are performed in left-to-right order.  Thus, for example,
       "cap_fowner+p-i" is equivalent to "cap_fowner+p cap_fowner-i".
       As another example, "cap_fowner+pe-i" and "cap_fowner=+pe" are

RETURN VALUE         top

       cap_from_text(), cap_to_text() and cap_to_name() return a non-
       NULL value on success, and NULL on failure.  cap_from_name()
       returns 0 for success, and -1 on failure (unknown capability).

       On failure, errno is set to EINVAL, or ENOMEM.

CONFORMING TO         top

       cap_from_text() and cap_to_text() are specified by the withdrawn
       POSIX.1e draft specification.  cap_from_name() and cap_to_name()
       are Linux extensions.

EXAMPLE         top

       The example program below demonstrates the use of cap_from_text()
       and cap_to_text().  The following shell session shows some
       example runs:

       $ ./a.out "cap_chown=p cap_chown+e"
       caps_to_text() returned "cap_chown=ep"
       $ ./a.out "all=pe cap_chown-e cap_kill-pe"
       caps_to_text() returned "=ep cap_chown-e cap_kill-ep"

       The source code of the program is as follows:

       #include <stdlib.h>
       #include <stdio.h>
       #include <sys/capability.h>

       #define handle_error(msg) \
           do { perror(msg); exit(EXIT_FAILURE); } while (0)

       main(int argc, char *argv[])
           cap_t caps;
           char *txt_caps;

           if (argc != 2) {
               fprintf(stderr, "%s <textual-cap-set>\n", argv[0]);

           caps = cap_from_text(argv[1]);
           if (caps == NULL)

           txt_caps = cap_to_text(caps, NULL);
           if (txt_caps == NULL)

           printf("caps_to_text() returned \"%s\"\n", txt_caps);

           if (cap_free(txt_caps) != 0 || cap_free(caps) != 0)


SEE ALSO         top

       libcap(3), cap_clear(3), cap_copy_ext(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
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-18.)  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

                               2022-09-22               CAP_FROM_TEXT(3)

Pages that refer to this page: capsh(1)cap_clear(3)cap_copy_ext(3)cap_get_file(3)cap_get_proc(3)cap_init(3)libcap(3)org.freedesktop.systemd1(5)systemd-system.conf(5)capabilities(7)captree(8)getcap(8)getpcaps(8)setcap(8)