Can rsync verify contents before syncing
Can Rsync be configured to verify the contents of the file before they are being synced. I have heard about checksum, but I came to know that checksum only does a sampling. I want to transfer a file only if it is contents are changed and not timestamp, is there a way to do it with any of the rsync modes. In my scenario, say file sample.text will be created every week and I want to sync it with a remote server only if the contents of sample.text are changed, since it is created every week, the time stamp would obviously change. But I want the transfer only on a content change.
Answer
Yes:
$ man rsync | grep "\--checksum"
-c, --checksum skip based on checksum, not mod-time & size
Rsync is pretty complicated. I recommend cuddle time with the man page and experimentation with test data before using it for anything remotely important.
Most of the time, people use rsync -ac source dest.
$ man rsync | grep "\--archive"
-a, --archive archive mode; same as -rlptgoD (no -H)
And that -rlptgoD garbage means: recursive (r), copy symlinks as symlinks (l), preserve permissions (p), preserve times (t), preserve group (g), preserve owner (o), preserve device files (D, super-user only), preserve special files (also part of D).
The -c or --checksum is really what you are looking for (skip based on checksum, not mod-time & size). Your supposition that rsync only samples mtime and size is wrong.