1CAP_FROM_TEXT(3)           Linux Programmer's Manual          CAP_FROM_TEXT(3)
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NAME

6       cap_from_text,  cap_to_text,  cap_to_name,  cap_from_name  - capability
7       state textual representation translation
8

SYNOPSIS

10       #include <sys/capability.h>
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12       cap_t cap_from_text(const char *buf_p);
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14       char *cap_to_text(cap_t caps, ssize_t *length_p);
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16       int cap_from_name(const char *name, cap_value_t *cap_p);
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18       char *cap_to_name(cap_value_t cap);
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20       Link with -lcap.
21

DESCRIPTION

23       These functions translate a capability state between an internal repre‐
24       sentation and a textual one.  The internal representation is managed by
25       the capability functions in working storage. The textual representation
26       is a structured, human-readable string suitable for display.
27
28       cap_from_text() allocates and initializes a capability state in working
29       storage. It then sets the contents of  this  newly  created  capability
30       state  to  the  state  represented  by a human-readable, nul-terminated
31       character string pointed to by buf_p.  It  returns  a  pointer  to  the
32       newly  created  capability state.  When the capability state in working
33       storage is no longer required, the caller should  free  any  releasable
34       memory  by  calling cap_free() with cap_t as an argument.  The function
35       returns an error if it cannot parse the contents of the string  pointed
36       to by buf_p or does not recognize any capability_name or flag character
37       as valid.  The function also returns an error if any flag is  both  set
38       and cleared within a single clause.
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40       cap_to_text()  converts the capability state in working storage identi‐
41       fied by cap_p into a nul-terminated human-readable string.  This  func‐
42       tion  allocates any memory necessary to contain the string, and returns
43       a pointer to the string.  If the pointer len_p is not NULL,  the  func‐
44       tion shall also return the full length of the string (not including the
45       nul terminator) in the location pointed to by  len_p.   The  capability
46       state  in  working  storage,  identified by cap_p, is completely repre‐
47       sented in the character string.  When the capability state  in  working
48       storage  is  no  longer required, the caller should free any releasable
49       memory by calling cap_free() with the returned  string  pointer  as  an
50       argument.
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52       cap_from_name() converts a text representation of a capability, such as
53       "cap_chown", to its numerical representation (CAP_CHOWN=0), writing the
54       decoded  value into *cap_p.  If cap_p is NULL no result is written, but
55       the return code of the function indicates whether or not the  specified
56       capability can be represented by the library.
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58       cap_to_name() converts a capability index value, cap, to a libcap-allo‐
59       cated  textual  string.  This  string  should   be   deallocated   with
60       cap_free().
61

TEXTUAL REPRESENTATION

63       A  textual  representation  of  capability sets consists of one or more
64       whitespace-separated clauses.  Each clause specifies some operations on
65       a capability set; the set starts out with all capabilities lowered, and
66       the meaning of the string is the state of the capability set after  all
67       the clauses have been applied in order.
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69       Each  clause consists of a list of comma-separated capability names (or
70       the word `all'), followed by an action-list.  An  action-list  consists
71       of  a  sequence of operator flag pairs.  Legal operators are: `=', '+',
72       and `-'.  Legal flags are: `e', `i', and `p'.  These  flags  are  case-
73       sensitive  and  specify  the  Effective, Inheritable and Permitted sets
74       respectively.
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76       In the capability name lists, all names are case-insensitive.  The spe‐
77       cial  name `all' specifies all capabilities; it is equivalent to a list
78       naming every capability individually.
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80       Unnamed capabilities can also be  specified  by  number.  This  feature
81       ensures that libcap can support capabilities that were not allocated at
82       the time libcap was compiled. However, generally upgrading libcap  will
83       add names for recently allocated capabilities.
84
85       The `=' operator indicates that the listed capabilities are first reset
86       in all three capability sets.  The subsequent flags (which are optional
87       when  associated with this operator) indicate that the listed capabili‐
88       ties for the corresponding set are to be raised.  For example:  "all=p"
89       means  lower every capability in the Effective and Inheritable sets but
90       raise all of the  Permitted  capabilities;  or,  "cap_fowner=ep"  means
91       raise  the  Effective and Permitted override-file-ownership capability,
92       while lowering this Inheritable capability.
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94       In the case that the leading operator is `=', and no list of  capabili‐
95       ties is provided, the action-list is assumed to refer to `all' capabil‐
96       ities.  For example, the following three clauses are equivalent to each
97       other  (and  indicate  a completely empty capability set): "all="; "=";
98       "cap_chown,<every-other-capability>=".
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100       The operators, `+' and `-' both require an explicit preceding  capabil‐
101       ity  list  and  one  or more explicit trailing flags.  The `+' operator
102       will raise all of the listed capabilities  in  the  flagged  capability
103       sets.   The  `-'  operator will lower all of the listed capabilities in
104       the flagged capability sets.  For example: "all+p" will  raise  all  of
105       the  Permitted  capabilities; "cap_fowner+p-i" will raise the override-
106       file-ownership capability in the Permitted  capability  set  and  lower
107       this Inheritable capability; "cap_fowner+pe-i" and "cap_fowner=+pe" are
108       equivalent.
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RETURN VALUE

111       cap_from_text(), cap_to_text()  and  cap_to_name()  return  a  non-NULL
112       value  on  success, and NULL on failure.  cap_from_name() returns 0 for
113       success, and -1 on failure (unknown capability).
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115       On failure, errno is set to EINVAL, or ENOMEM.
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CONFORMING TO

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

123       The example program below demonstrates the use of  cap_from_text()  and
124       cap_to_text().  The following shell session shows a some example runs:
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126           $ ./a.out "cap_chown=p cap_chown+e"
127           caps_to_text() returned "= cap_chown+ep"
128           $ ./a.out "all=pe cap_chown-e cap_kill-pe"
129           caps_to_text() returned "=ep cap_chown-e cap_kill-ep"
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131       The source code of the program is as follows:
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133       #include <stdlib.h>
134       #include <stdio.h>
135       #include <sys/capability.h>
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137       #define handle_error(msg) \
138           do { perror(msg); exit(EXIT_FAILURE); } while (0)
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140       int
141       main(int argc, char *argv[])
142       {
143           cap_t caps;
144           char *txt_caps;
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146           if (argc != 2) {
147               fprintf(stderr, "%s <textual-cap-set>\n", argv[0]);
148               exit(EXIT_FAILURE);
149           }
150
151           caps = cap_from_text(argv[1]);
152           if (caps == NULL)
153               handle_error("cap_from_text");
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155           txt_caps = cap_to_text(caps, NULL);
156           if (txt_caps == NULL)
157               handle_error("cap_to_text");
158
159           printf("caps_to_text() returned \"%s\"\n", txt_caps);
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161           if (cap_free(txt_caps) != 0 || cap_free(caps) != 0)
162               handle_error("cap_free");
163
164           exit(EXIT_SUCCESS);
165       }
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SEE ALSO

168       libcap(3),      cap_clear(3),      cap_compare(3),     cap_copy_ext(3),
169       cap_get_file(3), cap_get_proc(3), cap_init(3), capabilities(7)
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173                                  2008-05-10                  CAP_FROM_TEXT(3)
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