Exactly. But as I was looking it up, I was surprised to find the
warning in the sync(2) manpage that, although modern Linuxes now wait
till the write is complete before the system call returns, it's still
not safe to power down immediately because the data may be in the
drive's on-board cache and not yet on the drive's platters.
Mark
On 6/16/2012 2:03 PM, Jerry Feldman wrote:
On 06/16/2012 01:23 PM, Jack Coats wrote:
It may have been folk-lore, but the 'standard procedure' where I
worked, before shutting down a server on purpose, was, from root,
issue 3 commands separately when we wanted an orderly shutdown, but it
was 'urgent'.
sync
sync
halt
I am sure there is some basis in history that had a basis in fact at
the time. Even if the 'fact' was based on 'observation' rather than
reality.
See my other reply. With the old file systems, flushing and saving the
buffers was important, The halt(1) command was an immediate halt where
the Shutdown command was a script that did a sync. Generally with the
modern fast CPUs, kernels, and file systems, I don't think a sync will
buy you anything, but it will not cost you. In the olden days when you
used to do useful things, Unix systems were single CPU, and file systems
were slow. I think you remember the stone slab hard drives. What you did
not want it to halt in a partial write, then get into fsck hell.
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