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.