thread-keyring man page
thread-keyring — per-thread keyring
The thread keyring is a keyring used to anchor keys on behalf of a process. It is created only when a thread requests it. The thread keyring has the name (description) _tid.
A special serial number value, KEY_SPEC_THREAD_KEYRING, is defined that can be used in lieu of the actual serial number of the calling thread's thread keyring.
From the keyctl(1) utility, '@t' can be used instead of a numeric key ID in much the same way, but as keyctl(1) is a program run after forking, this is of no utility.
Thread keyrings are not inherited across clone(2) and fork(2) and are cleared by execve(2). A thread keyring is destroyed when the thread that refers to it terminates.
Initially, a thread does not have a thread keyring. If a thread doesn't have a thread keyring when it is accessed, then it will be created if it is to be modified; otherwise the operation fails with the error ENOKEY.
keyctl(1), keyctl(3), keyrings(7), persistent-keyring(7), process-keyring(7), session-keyring(7), user-keyring(7), user-session-keyring(7)
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add_key(2), keyctl(2), keyrings(7), keyutils(7), persistent-keyring(7), process-keyring(7), request_key(2), session-keyring(7), user-keyring(7), user-session-keyring(7).