PROCESS-KEYRING(7) Linux Programmer's Manual PROCESS-KEYRING(7)
process-keyring - per-process shared keyring
The process keyring is a keyring used to anchor keys on behalf of a process. It is created only when a process requests it. The process keyring has the name (description) _pid.
A special serial number value, KEY_SPEC_PROCESS_KEYRING, is defined that can be used in lieu of the actual serial number of the calling process's process keyring.
From the keyctl(1) utility, '@p' can be used instead of a numeric key ID in much the same way, but since keyctl(1) is a program run after forking, this is of no utility.
A thread created using the clone(2) CLONE_THREAD flag has the same process keyring as the caller of clone(2). When a new process is cre- ated using fork() it initially has no process keyring. A process's process keyring is cleared on execve(2). The process keyring is destroyed when the last thread that refers to it terminates.
If a process doesn't have a process keyring when it is accessed, then the process keyring will be created if the keyring is to be modified; otherwise, the error ENOKEY results.
keyctl(1), keyctl(3), keyrings(7), persistent-keyring(7), session-keyring(7), thread-keyring(7), user-keyring(7), user-session-keyring(7)
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Linux 2017-03-13 PROCESS-KEYRING(7)