man7/user-keyring.7

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  12 .TH "USER-KEYRING" 7 2017-03-13 Linux "Linux Programmer's Manual"
  13 .SH NAME
  14 user-keyring \- per-user keyring
  15 .SH DESCRIPTION
  16 The user keyring is a keyring used to anchor keys on behalf of a user.
  17 Each UID the kernel deals with has its own user keyring that
  18 is shared by all processes with that UID.
  19 The user keyring has a name (description) of the form
  20 .I _uid.<UID>
  21 where
  22 .I <UID>
  23 is the user ID of the corresponding user.
  24 .PP
  25 The user keyring is associated with the record that the kernel maintains
  26 for the UID.
  27 It comes into existence upon the first attempt to access either the
  28 user keyring, the
  29 .BR user-session-keyring (7),
  30 or the
  31 .BR session-keyring (7).
  32 The keyring remains pinned in existence so long as there are processes
  33 running with that real UID or files opened by those processes remain open.
  34 (The keyring can also be pinned indefinitely by linking it
  35 into another keyring.)
  36 .PP
  37 Typically, the user keyring is created by
  38 .BR pam_keyinit (8)
  39 when a user logs in.
  40 .PP
  41 The user keyring is not searched by default by
  42 .BR request_key (2).
  43 When
  44 .BR pam_keyinit (8)
  45 creates a session keyring, it adds to it a link to the user
  46 keyring so that the user keyring will be searched when the session keyring is.
  47 .PP
  48 A special serial number value,
  49 .BR KEY_SPEC_USER_KEYRING ,
  50 is defined that can be used in lieu of the actual serial number of
  51 the calling process's user keyring.
  52 .PP
  53 From the
  54 .BR keyctl (1)
  55 utility, '\fB@u\fP' can be used instead of a numeric key ID in
  56 much the same way.
  57 .PP
  58 User keyrings are independent of
  59 .BR clone (2),
  60 .BR fork (2),
  61 .BR vfork (2),
  62 .BR execve (2),
  63 and
  64 .BR _exit (2)
  65 excepting that the keyring is destroyed when the UID record is destroyed when
  66 the last process pinning it exits.
  67 .PP
  68 If it is necessary for a key associated with a user to exist beyond the UID
  69 record being garbage collected\(emfor example, for use by a
  70 .BR cron (8)
  71 script\(emthen the
  72 .BR persistent-keyring (7)
  73 should be used instead.
  74 .PP
  75 If a user keyring does not exist when it is accessed, it will be created.
  76 .SH SEE ALSO
  77 .ad l
  78 .nh
  79 .BR keyctl (1),
  80 .BR keyctl (3),
  81 .BR keyrings (7),
  82 .BR persistent\-keyring (7),
  83 .BR process\-keyring (7),
  84 .BR session\-keyring (7),
  85 .BR thread\-keyring (7),
  86 .BR user\-session\-keyring (7),
  87 .BR pam_keyinit (8)