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USER-KEYRING(7)            Linux Programmer's Manual           USER-KEYRING(7)
NAME
       user-keyring - per-user keyring
DESCRIPTION
       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-
       sponding user.
       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
       logs in.
       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
       keyring is.
       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-
       ated.
SEE ALSO
       keyctl(1), keyctl(3), keyrings(7), persistent-keyring(7),
       process-keyring(7), session-keyring(7), thread-keyring(7),
       user-session-keyring(7), pam_keyinit(8)
COLOPHON
       This page is part of release 4.15 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-KEYRING(7)