Linux system clock divided clock (System Clock) and hardware (Real Time Clock, referred to as RTC) clock. Refers to the current system clock is the clock in Linux Kernel, and the hardware on the motherboard clock is battery-powered clock, the hardware clock can be set in the BIOS. When Linux boots, to read the hardware clock is the system clock is set, then the system clock will operate independent of the hardware.
Linux all commands (including functions) are employed to set the system clock. In Linux, for view and set clock command mainly date, hwclock and clock. Which, clock and hwclock usage is similar, only one on the line, but the clock command in addition to support for x86 hardware systems, also supports Alpha hardware architecture.