TuxForLife的答案很好，但我强烈建议您-c在本地同步时使用。您可以辩解说，为远程同步这样做不值得花费时间/网络代价，但是对于本地文件来说完全值得，因为速度是如此之快。
-c, --checksum
This forces the sender to checksum every regular file using a 128-bit MD4
checksum. It does this during the initial file-system scan as it builds
the list of all available files. The receiver then checksums its version
of each file (if it exists and it has the same size as its sender-side
counterpart) in order to decide which files need to be updated: files with
either a changed size or a changed checksum are selected for transfer.
Since this whole-file checksumming of all files on both sides of the con-
nection occurs in addition to the automatic checksum verifications that
occur during a file's transfer, this option can be quite slow.
Note that rsync always verifies that each transferred file was correctly
reconstructed on the receiving side by checking its whole-file checksum,
but that automatic after-the-transfer verification has nothing to do with
this option's before-the-transfer "Does this file need to be updated?"
check.
这显示了具有相同大小和时间戳的方法会使您失败。
设置
$ cd /tmp
$ mkdir -p {A,b}/1/2/{3,4}
$ echo "\___________from A" | \
tee A/1/2/x | tee A/1/2/3/y | tee A/1/2/4/z | \
tr A b | \
tee b/1/2/x | tee b/1/2/3/y | tee b/1/2/4/z | \
tee b/1/2/x0 | tee b/1/2/3/y0 > b/1/2/4/z0
$ find A b -type f | xargs -I% sh -c "echo %; cat %;"
A/1/2/3/y
\___________from A
A/1/2/4/z
\___________from A
A/1/2/x
\___________from A
b/1/2/3/y
\___________from b
b/1/2/3/y0
\___________from b
b/1/2/4/z
\___________from b
b/1/2/4/z0
\___________from b
b/1/2/x
\___________from b
b/1/2/x0
\___________from b
rsync不复制任何内容，因为文件都具有相同的大小和时间戳
$ rsync -avu A/ b
building file list ... done
sent 138 bytes received 20 bytes 316.00 bytes/sec
total size is 57 speedup is 0.36
$ find A b -type f | xargs -I% sh -c "echo %; cat %;"
A/1/2/3/y
\___________from A
A/1/2/4/z
\___________from A
A/1/2/x
\___________from A
b/1/2/3/y
\___________from b
b/1/2/3/y0
\___________from b
b/1/2/4/z
\___________from b
b/1/2/4/z0
\___________from b
b/1/2/x
\___________from b
b/1/2/x0
\___________from b
正确工作的rsync，因为它比较校验和
$ rsync -cavu A/ b
building file list ... done
1/2/x
1/2/3/y
1/2/4/z
sent 381 bytes received 86 bytes 934.00 bytes/sec
total size is 57 speedup is 0.12
$ find A b -type f | xargs -I% sh -c "echo %; cat %;"
A/1/2/3/y
\___________from A
A/1/2/4/z
\___________from A
A/1/2/x
\___________from A
b/1/2/3/y
\___________from A
b/1/2/3/y0
\___________from b
b/1/2/4/z
\___________from A
b/1/2/4/z0
\___________from b
b/1/2/x
\___________from A
b/1/2/x0
\___________from b
