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USER-SESSION-KEYRING(7) Linux Programmer's Manual USER-SESSION-KEYRING(7)

NAME

     user-session-keyring - per-user default session keyring

DESCRIPTION

     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 ses-
     sion 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 cre-
     ated 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  recom-
     mended--especially  if  the process is running as root--that a session-
     keyring(7) be set explicitly, for example by pam_keyinit(8).

NOTES

     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).