docs: fix and reword --update docs

After discussion on the forum with @bandwidth, this rewords the
--update docs to be correct and easier to understand.

See: https://forum.rclone.org/t/help-understanding-update/28937
This commit is contained in:
Nick Craig-Wood 2022-01-31 17:09:11 +00:00
parent 051685baa1
commit 0ae39bda8d

View file

@ -1791,24 +1791,30 @@ The default is to run 4 file transfers in parallel.
This forces rclone to skip any files which exist on the destination
and have a modified time that is newer than the source file.
This can be useful when transferring to a remote which doesn't support
mod times directly (or when using `--use-server-modtime` to avoid extra
API calls) as it is more accurate than a `--size-only` check and faster
than using `--checksum`.
This can be useful in avoiding needless transfers when transferring to
a remote which doesn't support modification times directly (or when
using `--use-server-modtime` to avoid extra API calls) as it is more
accurate than a `--size-only` check and faster than using
`--checksum`. On such remotes (or when using `--use-server-modtime`)
the time checked will be the uploaded time.
If an existing destination file has a modification time older than the
source file's, it will be updated if the sizes are different. If the
sizes are the same, it will be updated if the checksum is different or
not available.
If an existing destination file has a modification time equal (within
the computed modify window precision) to the source file's, it will be
updated if the sizes are different. If `--checksum` is set then
rclone will update the destination if the checksums differ too.
the computed modify window) to the source file's, it will be updated
if the sizes are different. The checksum will not be checked in this
case unless the `--checksum` flag is provided.
If an existing destination file is older than the source file then
it will be updated if the size or checksum differs from the source file.
In all other cases the file will not be updated.
On remotes which don't support mod time directly (or when using
`--use-server-modtime`) the time checked will be the uploaded time.
This means that if uploading to one of these remotes, rclone will skip
any files which exist on the destination and have an uploaded time that
is newer than the modification time of the source file.
Consider using the `--modify-window` flag to compensate for time skews
between the source and the backend, for backends that do not support
mod times, and instead use uploaded times. However, if the backend
does not support checksums, note that sync'ing or copying within the
time skew window may still result in additional transfers for safety.
### --use-mmap ###