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The identifier for the system-wide monotonic clock, which is defined as a clock measuring real time, whose value cannot be set via clock_settime and which cannot have negative clock jumps. The maximum possible clock jump shall be implementation defined. For this clock, the value returned by getTime represents the amount of time (in seconds and nanoseconds) since an unspecified point in the past (for example, system start-up time, or the Epoch). This point does not change after system start-up time. Note that the absolute value of the monotonic clock is meaningless (because its origin is arbitrary), and thus there is no need to set it. Furthermore, realtime applications can rely on the fact that the value of this clock is never set.

The identifier of the system-wide clock measuring real time. For this clock, the value returned by getTime represents the amount of time (in seconds and nanoseconds) since the Epoch.

The identifier of the CPU-time clock associated with the calling process. For this clock, the value returned by getTime represents the amount of execution time of the current process.

The identifier of the CPU-time clock associated with the calling OS thread. For this clock, the value returned by getTime represents the amount of execution time of the current OS thread.

(since Linux 2.6.28; Linux-specific) Similar to CLOCK_MONOTONIC, but provides access to a raw hardware-based time that is not subject to NTP adjustments or the incremental adjustments performed by adjtime(3).

(since Linux 2.6.39; Linux-specific) Identical to CLOCK_MONOTONIC, except it also includes any time that the system is suspended. This allows applications to get a suspend-aware monotonic clock without having to deal with the complications of CLOCK_REALTIME, which may have discontinuities if the time is changed using settimeofday(2).

(since Linux 2.6.32; Linux-specific) A faster but less precise version of CLOCK_MONOTONIC. Use when you need very fast, but not fine-grained timestamps.

(since Linux 2.6.32; Linux-specific) A faster but less precise version of CLOCK_REALTIME. Use when you need very fast, but not fine-grained timestamps.