USER-KEYRING(7) Linux Programmer's Manual USER-KEYRING(7)
user-keyring - per-user keyring
The user keyring is a keyring used to anchor keys on behalf of a user.
Each UID the kernel deals with has its own user keyring that is shared
by all processes with that UID. The user keyring has a name (descrip‐
tion) of the form _uid.<UID> where <UID> is the user ID of the corre‐
The user keyring is associated with the record that the kernel main‐
tains for the UID. It comes into existence upon the first attempt to
access either the user keyring, the user-session-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.)
Typically, the user keyring is created by pam_keyinit(8) when a user
The user keyring is not searched by default by request_key(2). When
pam_keyinit(8) creates a session keyring, it adds to it a link to the
user keyring so that the user keyring will be searched when the session
A special serial number value, KEY_SPEC_USER_KEYRING, is defined that
can be used in lieu of the actual serial number of the calling
process's user keyring.
From the keyctl(1) utility, '@u' can be used instead of a numeric key
ID in much the same way.
User 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 it is necessary for a key associated with a user to exist beyond the
UID record being garbage collected—for example, for use by a cron(8)
script—then the persistent-keyring(7) should be used instead.
If a user keyring does not exist when it is accessed, it will be cre‐
keyctl(1), keyctl(3), keyrings(7), persistent-keyring(7),
process-keyring(7), session-keyring(7), thread-keyring(7),
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Linux 2017-03-13 USER-KEYRING(7)