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might as well include the first paragraph too, since it mentions the waiting the second refers to

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edited Oct 20, 2024 at 13:51

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From FreeBSD sync(8) History:

…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.

Issuing three separate syncsync 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)reboot(2) and sync(2)sync(2) which rendered this trick obsolete.

sync.8: Document that the "sync dance" is not a thing · freebsd/freebsd-src@177ba18 (2024-04-25) refers to https://reviews.freebsd.org/D33233 (2021).

Manual pages for 4.3BSD NET/2:

From FreeBSD sync(8) History:

… 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.

sync.8: Document that the "sync dance" is not a thing · freebsd/freebsd-src@177ba18 (2024-04-25) refers to https://reviews.freebsd.org/D33233 (2021).

Manual pages for 4.3BSD NET/2:

From FreeBSD sync(8) History:

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.

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.

sync.8: Document that the "sync dance" is not a thing · freebsd/freebsd-src@177ba18 (2024-04-25) refers to https://reviews.freebsd.org/D33233 (2021).

Manual pages for 4.3BSD NET/2:

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answered Oct 20, 2024 at 13:33

Graham Perrin

From FreeBSD sync(8) History:

… 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.

sync.8: Document that the "sync dance" is not a thing · freebsd/freebsd-src@177ba18 (2024-04-25) refers to https://reviews.freebsd.org/D33233 (2021).

Manual pages for 4.3BSD NET/2: