terminalid

Terminalid is a general term used to denote a unique identifier assigned to a terminal interface or session within a computing environment. It is used to distinguish concurrent input and output channels, track activity, and associate actions with a specific terminal or session.

In Unix-like systems, the concept manifests as the controlling terminal of a process, commonly represented by a device file such as /dev/pts/3 or /dev/tty1. The kernel binds a session to a terminal and record-keeping utilities log this terminal identifier in files such as utmp and wtmp, where the 'line' or 'tty' field serves as the terminal id for the session. When a user connects via SSH or opens a local terminal, the system allocates a pseudo-terminal (pty) with a unique port of /dev/pts; that path functions as the terminal id for that session.

In networked contexts, terminal IDs are used by server processes to apply per-terminal policies, isolate session resources, and facilitate auditing. Some programs expose or log the terminal id to correlate events with a particular login. In Windows, similar constructs exist as session IDs for Terminal Services or Remote Desktop, but the term terminalid is not a formal standard there.

Because there is no universal standard called "terminalid", implementations differ; in many contexts the more precise terms are terminal device name (such as /dev/pts/3), controlling terminal, session ID, or login line. The TERM environment variable identifies terminal capabilities, not identity.

See also utmp, wtmp, login, SSH, pty, tty.