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Manual Pages  — SYNC

NAME

sync – force completion of pending disk writes (flush cache)

CONTENTS

SYNOPSIS


sync

DESCRIPTION

The sync utility can be called to ensure that all disk writes have been completed before the processor is halted in a way not suitably done by reboot(8) or halt(8). Generally, it is preferable to use reboot(8) or halt(8) to shut down the system, as they may perform additional actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync.

The sync utility utilizes the sync(2) function call.

SEE ALSO

fsync(2), sync(2), syncer(4), halt(8), reboot(8)

HISTORY

A sync utility appeared in AT&T v4 .

On systems older than BSD 4.0, commands like reboot(8) and halt(8) were unavailable. The shutdown procedure involved running sync, waiting for the lights to stop, and turning off the machine.

Issuing three separate sync commands (one line each) was a placebo that would generally suffice in AT&T v7 machines that were otherwise quiesced systems. It replaced the one-per-line sync as a substitute for waiting.

BSD 4.0 introduced reboot(2) and sync(2) which rendered this trick obsolete.

SYNC (8) April 25, 2024
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