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USER-SESSION-KEYRING(7) Linux Programmer's ManualUSER-SESSION-KEYRING(7)
user-session-keyring - per-user default session keyring
The user session keyring is a keyring used to anchor keys on
behalf of a user. Each UID the kernel deals with has its own
user session keyring that is shared by all processes with that
UID. The user session keyring has a name (description) of the
form _uid_ses.<UID> where <UID> is the user ID of the
corresponding user.
The user session keyring is associated with the record that the
kernel maintains for the UID. It comes into existence upon the
first attempt to access either the user session keyring, the
user-keyring(7), or the session-keyring(7). The keyring remains
pinned in existence so long as there are processes running with
that real UID or files opened by those processes remain open.
(The keyring can also be pinned indefinitely by linking it into
another keyring.)
The user session keyring is created on demand when a thread
requests it or when a thread asks for its session-keyring(7) and
that keyring doesn't exist. In the latter case, a user session
keyring will be created and, if the session keyring wasn't to be
created, the user session keyring will be set as the process's
actual session keyring.
The user session keyring is searched by request_key(2) if the
actual session keyring does not exist and is ignored otherwise.
A special serial number value, KEY_SPEC_USER_SESSION_KEYRING, is
defined that can be used in lieu of the actual serial number of
the calling process's user session keyring.
From the keyctl(1) utility, '@us' can be used instead of a
numeric key ID in much the same way.
User session keyrings are independent of clone(2), fork(2),
vfork(2), execve(2), and _exit(2) excepting that the keyring is
destroyed when the UID record is destroyed when the last process
pinning it exits.
If a user session keyring does not exist when it is accessed, it
will be created.
Rather than relying on the user session keyring, it is strongly
recommended—especially if the process is running as root—that a
session-keyring(7) be set explicitly, for example by
pam_keyinit(8).
The user session keyring was added to support situations where a
process doesn't have a session keyring, perhaps because it was
created via a pathway that didn't involve PAM (e.g., perhaps it
was a daemon started by inetd(8)). In such a scenario, the user
session keyring acts as a substitute for the session-keyring(7).
keyctl(1), keyctl(3), keyrings(7), persistent-keyring(7),
process-keyring(7), session-keyring(7), thread-keyring(7),
user-keyring(7)
This page is part of release 5.13 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
https://www.kernel.org/doc/man-pages/.
Linux 2020-08-13 USER-SESSION-KEYRING(7)
Pages that refer to this page: add_key(2), keyctl(2), request_key(2), keyctl_join_session_keyring(3), keyctl_session_to_parent(3), keyrings(7), keyutils(7), persistent-keyring(7), process-keyring(7), session-keyring(7), thread-keyring(7), user-keyring(7), pam_keyinit(8)
Copyright and license for this manual page
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