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NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON |
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persist...keyring(7) Miscellaneous Information Manualpersist...keyring(7)
persistent-keyring - per-user persistent keyring
The persistent keyring is a keyring used to anchor keys on behalf
of a user. Each UID the kernel deals with has its own persistent
keyring that is shared between all threads owned by that UID. The
persistent keyring has a name (description) of the form
_persistent.<UID> where <UID> is the user ID of the corresponding
user.
The persistent keyring may not be accessed directly, even by
processes with the appropriate UID. Instead, it must first be
linked to one of a process's keyrings, before that keyring can
access the persistent keyring by virtue of its possessor permits.
This linking is done with the keyctl_get_persistent(3) function.
If a persistent keyring does not exist when it is accessed by the
keyctl_get_persistent(3) operation, it will be automatically
created.
Each time the keyctl_get_persistent(3) operation is performed, the
persistent keyring's expiration timer is reset to the value in:
/proc/sys/kernel/keys/persistent_keyring_expiry
Should the timeout be reached, the persistent keyring will be
removed and everything it pins can then be garbage collected. The
keyring will then be re-created on a subsequent call to
keyctl_get_persistent(3).
The persistent keyring is not directly searched by request_key(2);
it is searched only if it is linked into one of the keyrings that
is searched by request_key(2).
The persistent keyring is independent of clone(2), fork(2),
vfork(2), execve(2), and _exit(2). It persists until its
expiration timer triggers, at which point it is garbage collected.
This allows the persistent keyring to carry keys beyond the life
of the kernel's record of the corresponding UID (the destruction
of which results in the destruction of the user-keyring(7) and the
user-session-keyring(7)). The persistent keyring can thus be used
to hold authentication tokens for processes that run without user
interaction, such as programs started by cron(8).
The persistent keyring is used to store UID-specific objects that
themselves have limited lifetimes (e.g., kerberos tokens). If
those tokens cease to be used (i.e., the persistent keyring is not
accessed), then the timeout of the persistent keyring ensures that
the corresponding objects are automatically discarded.
Special operations
The keyutils library provides the keyctl_get_persistent(3)
function for manipulating persistent keyrings. (This function is
an interface to the keyctl(2) KEYCTL_GET_PERSISTENT operation.)
This operation allows the calling thread to get the persistent
keyring corresponding to its own UID or, if the thread has the
CAP_SETUID capability, the persistent keyring corresponding to
some other UID in the same user namespace.
Each user namespace owns a keyring called .persistent_register
that contains links to all of the persistent keys in that
namespace. (The .persistent_register keyring can be seen when
reading the contents of the /proc/keys file for the UID 0 in the
namespace.) The keyctl_get_persistent(3) operation looks for a
key with a name of the form _persistent.UID in that keyring,
creates the key if it does not exist, and links it into the
keyring.
keyctl(1), keyctl(3), keyctl_get_persistent(3), keyrings(7),
process-keyring(7), session-keyring(7), thread-keyring(7),
user-keyring(7), user-session-keyring(7)
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 2025-05-17 persist...keyring(7)
Pages that refer to this page: add_key(2), keyctl(2), KEYCTL_GET_PERSISTENT(2const), request_key(2), keyctl_get_persistent(3), keyrings(7), keyutils(7), process-keyring(7), session-keyring(7), thread-keyring(7), user-keyring(7), user-session-keyring(7)
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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. |
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