SYNC(8)

💖 NAME 💖

okay so welcome to SYNC(8) from the System Manager's Manual, bestie — this is the lil page for the sync utility. The name section is literally:

• sync — force completion of pending disk writes (flush cache)

no cap, that's the whole vibe: it makes pending disk writes finish and flushes the cache. ✨

✨ SYNOPSIS ✨

sync

that's it. one word, main character energy, periodt. 💅

🌸 DESCRIPTION 🌸

Okay so you can call the sync utility to ensure that all disk writes have been completed before the processor is halted in a way that isn't suitably done by reboot(8) or halt(8). Basically it's the “make sure the writes actually landed” girlie. 🫶

Generally, it's preferable to use reboot(8) or halt(8) to shut down the system, because they may perform additional actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync. So like, let the shutdown besties do their extra steps, iykyk. 💜

Under the hood, the sync utility utilizes the sync(2) function call. That's the whole tea. 🍓

🦋 SEE ALSO 🦋

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

go read these if you want the full lore. slay. 🌈

🎀 HISTORY 🎀

A sync utility appeared in Version 4 AT&T UNIX. So like, she's been iconic since forever. 👑

On systems older than 4.0BSD, 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. Literally: run sync, stare at the lights, then power down. 😭

Issuing three separate sync commands (one line each) was a placebo that would generally suffice in Version 7 AT&T UNIX machines that were otherwise quiesced systems. It replaced the one-per-line sync as a substitute for waiting.

4.0BSD introduced reboot(2) and sync(2) which rendered this trick obsolete. so the three-sync placebo era was over, periodt. 💀

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later, bestie! this page is from Debian, dated April 25, 2024, and it's the SYNC(8) manual page. slay, and may your pending disk writes be ever completed. 💅🎀