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       add_key - add a key to the kernel's key management facility


       #include <sys/types.h>
       #include <keyutils.h>

       key_serial_t add_key(const char *type, const char *description,
                            const void *payload, size_t plen,
                            key_serial_t keyring);

       No glibc wrapper is provided for this system call; see NOTES.


       add_key() creates or updates a key of the given type and description, instantiates it with
       the payload of length plen, attaches it to the nominated keyring, and  returns  the  key's
       serial number.

       The  key  may  be rejected if the provided data is in the wrong format or it is invalid in
       some other way.

       If the destination keyring already contains a key that  matches  the  specified  type  and
       description, then, if the key type supports it, that key will be updated rather than a new
       key being created; if not, a new key (with a different ID) will be  created  and  it  will
       displace the link to the extant key from the keyring.

       The  destination keyring serial number may be that of a valid keyring for which the caller
       has write permission.  Alternatively, it may be one of the following special keyring IDs:

              This specifies the caller's thread-specific keyring (thread-keyring(7)).

              This specifies the caller's process-specific keyring (process-keyring(7)).

              This specifies the caller's session-specific keyring (session-keyring(7)).

              This specifies the caller's UID-specific keyring (user-keyring(7)).

              This specifies the caller's UID-session keyring (user-session-keyring(7)).

   Key types
       The key type is a string that specifies the key's type.  Internally, the kernel defines  a
       number  of  key types that are available in the core key management code.  Among the types
       that are available for user-space use and  can  be  specified  as  the  type  argument  to
       add_key() are the following:

              Keyrings are special key types that may contain links to sequences of other keys of
              any type.  If this interface is used to create a keyring, then  payload  should  be
              NULL and plen should be zero.

       "user" This  is  a general purpose key type whose payload may be read and updated by user-
              space applications.  The key is kept entirely within kernel  memory.   The  payload
              for keys of this type is a blob of arbitrary data of up to 32,767 bytes.

       "logon" (since Linux 3.3)
              This  key type is essentially the same as "user", but it does not permit the key to
              read.  This is suitable for storing payloads that you do not want  to  be  readable
              from user space.

       This  key  type vets the description to ensure that it is qualified by a "service" prefix,
       by checking to ensure that the description contains  a  ':'  that  is  preceded  by  other

       "big_key" (since Linux 3.13)
              This  key type is similar to "user", but may hold a payload of up to 1 MiB.  If the
              key payload is large enough, then it may be stored encrypted in tmpfs (which can be
              swapped out) rather than kernel memory.

       For further details on these key types, see keyrings(7).


       On  success,  add_key()  returns  the  serial number of the key it created or updated.  On
       error, -1 is returned and errno is set to indicate the cause of the error.


       EACCES The keyring wasn't available for modification by the user.

       EDQUOT The key quota for this user would be exceeded by creating this key or linking it to
              the keyring.

       EFAULT One  or  more of type, description, and payload points outside process's accessible
              address space.

       EINVAL The size of the string (including the terminating null byte) specified in  type  or
              description exceeded the limit (32 bytes and 4096 bytes respectively).

       EINVAL The payload data was invalid.

       EINVAL type  was "logon" and the description was not qualified with a prefix string of the
              form "service:".

              The keyring has expired.

              The keyring has been revoked.

       ENOKEY The keyring doesn't exist.

       ENOMEM Insufficient memory to create a key.

       EPERM  The type started with a period ('.').  Key types  that  begin  with  a  period  are
              reserved to the implementation.

       EPERM  type  was "keyring" and the description started with a period ('.').  Keyrings with
              descriptions (names) that begin with a period are reserved to the implementation.


       This system call first appeared in Linux 2.6.10.


       This system call is a nonstandard Linux extension.


       No wrapper for this system call is provided in  glibc.   A  wrapper  is  provided  in  the
       libkeyutils package.  When employing the wrapper in that library, link with -lkeyutils.


       The  program  below creates a key with the type, description, and payload specified in its
       command-line arguments, and links that key into the session keyring.  The following  shell
       session demonstrates the use of the program:

           $ ./a.out user mykey "Some payload"
           Key ID is 64a4dca
           $ grep '64a4dca' /proc/keys
           064a4dca I--Q---    1 perm 3f010000  1000  1000 user    mykey: 12

   Program source

       #include <sys/types.h>
       #include <keyutils.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       main(int argc, char *argv[])
           key_serial_t key;

           if (argc != 4) {
               fprintf(stderr, "Usage: %s type description payload\n",

           key = add_key(argv[1], argv[2], argv[3], strlen(argv[3]),
           if (key == -1) {

           printf("Key ID is %lx\n", (long) key);



       keyctl(1), keyctl(2), request_key(2), keyctl(3), keyrings(7), keyutils(7),
       persistent-keyring(7), process-keyring(7), session-keyring(7), thread-keyring(7),
       user-keyring(7), user-session-keyring(7)

       The kernel source files Documentation/security/keys/core.rst and
       Documentation/keys/request-key.rst (or, before Linux 4.13, in the files
       Documentation/security/keys.txt and Documentation/security/keys-request-key.txt).


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