|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
add_key(2) System Calls Manual add_key(2)
add_key - add a key to the kernel's key management facility
Standard C library (libc, -lc)
#include <keyutils.h>
key_serial_t add_key(size_t size;
const char *type, const char *description,
const void payload[size], size_t size,
key_serial_t keyring);
Note: There is no glibc wrapper 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 size size,
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:
KEY_SPEC_THREAD_KEYRING
This specifies the caller's thread-specific keyring
(thread-keyring(7)).
KEY_SPEC_PROCESS_KEYRING
This specifies the caller's process-specific keyring
(process-keyring(7)).
KEY_SPEC_SESSION_KEYRING
This specifies the caller's session-specific keyring
(session-keyring(7)).
KEY_SPEC_USER_KEYRING
This specifies the caller's UID-specific keyring
(user-keyring(7)).
KEY_SPEC_USER_SESSION_KEYRING
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:
"keyring"
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
size 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 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 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:".
EKEYEXPIRED
The keyring has expired.
EKEYREVOKED
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.
Linux.
Linux 2.6.10.
glibc does not provide a wrapper for this system call. A wrapper
is provided in the libkeyutils library. (The accompanying package
provides the <keyutils.h> header file.) 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 <keyutils.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(int argc, char *argv[])
{
key_serial_t key;
if (argc != 4) {
fprintf(stderr, "Usage: %s type description payload\n",
argv[0]);
exit(EXIT_FAILURE);
}
key = add_key(argv[1], argv[2], argv[3], strlen(argv[3]),
KEY_SPEC_SESSION_KEYRING);
if (key == -1) {
perror("add_key");
exit(EXIT_FAILURE);
}
printf("Key ID is %jx\n", (uintmax_t) key);
exit(EXIT_SUCCESS);
}
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).
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. 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
[email protected]
Linux man-pages 6.15 2025-06-28 add_key(2)
Pages that refer to this page: keyctl(2), request_key(2), syscalls(2), keyctl(3), keyctl_capabilities(3), keyctl_chown(3), keyctl_clear(3), keyctl_describe(3), keyctl_get_keyring_ID(3), keyctl_get_persistent(3), keyctl_get_security(3), keyctl_instantiate(3), keyctl_invalidate(3), keyctl_join_session_keyring(3), keyctl_link(3), keyctl_move(3), keyctl_pkey_encrypt(3), keyctl_pkey_query(3), keyctl_pkey_sign(3), keyctl_read(3), keyctl_revoke(3), keyctl_search(3), keyctl_session_to_parent(3), keyctl_setperm(3), keyctl_set_reqkey_keyring(3), keyctl_set_timeout(3), keyctl_update(3), keyctl_watch_key(3), proc_pid_attr(5), asymmetric-key(7), keyrings(7), keyutils(7)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|