hostid

Display the numeric identifier for the current host in hexadecimal

$ hostid

hostid

The `hostid` command displays the numeric identifier (in hexadecimal) for the current host machine. This identifier is derived from the machine's hardware or software configuration. It is often used in software licensing or other situations where a unique machine identifier is needed. The identifier is useful for uniquely identifying a system. On some systems, if no suitable identifier is found, `hostid` will generate a pseudo-random number based on the current time. This behavior varies depending on the specific implementation of `hostid` on the system.
Note:The same id can be assigned to different hosts. Check caveats.

The `hostid` command's output is not guaranteed to be globally unique, especially in virtualized environments or on systems where hardware IDs are easily modified. Relying solely on `hostid` for critical security purposes is discouraged. There might be collisions where different physical systems report the same `hostid`, especially in cloud environments. In some instances, it returns the IP address of the host as a hex number.

The `hostid` command typically returns an exit status of 0 on success and a non-zero exit status if it encounters an error (e.g., unable to determine the host ID).

The `hostid` command has been a part of Unix-like operating systems for a long time and standardized by POSIX. The original purpose of the command was to provide a relatively easy way to differentiate physical machines within a network. Over time, the significance of the `hostid` has diminished due to the rise of virtual machines, containerization, and cloud computing, where hardware identifiers are frequently virtualized and can change.

uname(1), hostname(1)