-a, --archive
This is equivalent to -rlptgoD. It is a quick way of saying you want recursion and want to
preserve almost everything (with -H being a notable omission). The only exception to the above
equivalence is when --files-from is specified, in which case -r is not implied.
Note that -a does not preserve hardlinks, because finding multiply-linked files is expensive. You
must separately specify -H.
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-H, --hard-links
This tells rsync to look for hard-linked files in the source and link together the corresponding
files on the destination. Without this option, hard-linked files in the source are treated as
though they were separate files.
This option does NOT necessarily ensure that the pattern of hard links on the destination exactly
matches that on the source. Cases in which the destination may end up with extra hard links
include the following:
o If the destination contains extraneous hard-links (more linking than what is present in the
source file list), the copying algorithm will not break them explicitly. However, if one
or more of the paths have content differences, the normal file-update process will break
those extra links (unless you are using the --inplace option).
o If you specify a --link-dest directory that contains hard links, the linking of the
destination files against the --link-dest files can cause some paths in the destination to
become linked together due to the --link-dest associations.
Note that rsync can only detect hard links between files that are inside the transfer set. If
rsync updates a file that has extra hard-link connections to files outside the transfer, that
linkage will be broken. If you are tempted to use the --inplace option to avoid this breakage, be
very careful that you know how your files are being updated so that you are certain that no
unintended changes happen due to lingering hard links (and see the --inplace option for more
caveats).
If incremental recursion is active (see --recursive), rsync may transfer a missing hard-linked
file before it finds that another link for that contents exists elsewhere in the hierarchy. This
does not affect the accuracy of the transfer (i.e. which files are hard-linked together), just its
efficiency (i.e. copying the data for a new, early copy of a hard-linked file that could have been
found later in the transfer in another member of the hard-linked set of files). One way to avoid
this inefficiency is to disable incremental recursion using the --no-inc-recursive option.
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--delete
This tells rsync to delete extraneous files from the receiving side (ones that aren’t on the
sending side), but only for the directories that are being synchronized. You must have asked
rsync to send the whole directory (e.g. "dir" or "dir/") without using a wildcard for the
directory’s contents (e.g. "dir/*") since the wildcard is expanded by the shell and rsync thus
gets a request to transfer individual files, not the files’ parent directory. Files that are
excluded from the transfer are also excluded from being deleted unless you use the
--delete-excluded option or mark the rules as only matching on the sending side (see the
include/exclude modifiers in the FILTER RULES section).
Prior to rsync 2.6.7, this option would have no effect unless --recursive was enabled. Beginning
with 2.6.7, deletions will also occur when --dirs (-d) is enabled, but only for directories whose
contents are being copied.
This option can be dangerous if used incorrectly! It is a very good idea to first try a run using
the --dry-run option (-n) to see what files are going to be deleted.
If the sending side detects any I/O errors, then the deletion of any files at the destination will
be automatically disabled. This is to prevent temporary filesystem failures (such as NFS errors)
on the sending side from causing a massive deletion of files on the destination. You can override
this with the --ignore-errors option.
The --delete option may be combined with one of the --delete-WHEN options without conflict, as
well as --delete-excluded. However, if none of the --delete-WHEN options are specified, rsync
will choose the --delete-during algorithm when talking to rsync 3.0.0 or newer, and the
--delete-before algorithm when talking to an older rsync. See also --delete-delay and
--delete-after.
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