BOOTID

BOOTID, or boot_id, is a per-boot unique identifier used by modern Linux environments and related logging systems to label a single boot session. It enables correlating events, logs, and traces that belong to the same startup and distinguishing them from other boots.

In Linux systems, the boot_id is generated at boot and exposed via the file /proc/sys/kernel/random/boot_id. The value is a UUID that remains constant for the entire lifecycle of a single boot and changes on every reboot. Systemd-enabled systems use this identifier to tag journal entries and support commands such as journalctl --list-boots or journalctl -b to reference a particular boot by its ID or position.

Relation to other identifiers: The boot_id is distinct from the machine-id, which is a persistent system-wide identifier that remains the same across reboots. While boot_id changes after each restart, machine-id generally persists unless reset or reinstalled.

Context and limitations: In containerized environments, the boot_id seen by a container typically reflects the host boot, since the container shares the host kernel. Boot_id is not intended as a security token or authentication credential; it is a diagnostic aid for debugging, auditing, and log correlation.

See also: Linux kernel /proc/sys/kernel/random/boot_id, systemd, journald, machine-id.