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. This
keyring is associated with the record that the kernel maintains for the UID
and, once created, is retained as long as that record persists. It is shared
amongst all processes of that UID.
The user session keyring is created on demand when a thread requests it or when
a thread asks for its session keyring
and that 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
() 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 calling process's user session keyring's
actual serial number.
From the keyctl utility, ' @us
' can be used instead of a numeric key ID
in much the same way.
User session keyrings are independent of clone(), fork(), vfork(), execve() and
exit() 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
It is strongly recommended that a session keyring
be set explicitly, for
example by pam_keyinit
, rather than relying on the user session keyring
- particularly if a process is running as root.