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NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON |
USER-SESSION-KEYRING(7) Linux Programmer's Manual USER-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 4.12 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 2017-03-13 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)