ADD_KEY(2)                Linux Key Management Calls                ADD_KEY(2)

       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-

              This  specifies  the caller's process-specific keyring (process-

              This specifies the caller's session-specific  keyring  (session-

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

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

   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 fol-

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

       "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 characters.

       "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 pe-
              riod 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),

       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

       This page is part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2019-03-06                        ADD_KEY(2)
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