The problem#
When running an incremental backup with rsync with the
--progress flag, it often spends lot of time outputting nothing as it
scans through many unchanged files. If you think of it before starting
the transfer, --info=progress2 or the name2/skip2 --info flags
would give more detail, but once the transfer has been going for a
while, you probably don't want to cancel and restart it so you can add
those flags.
The solution#
The documentation and this StackExchange answer
say you can send a SIGVTALRM signal to rsync version 3.2.0+ and
it will output its current progress, but that wasn't working for me.
As a workaround, you can use strace to get a running log
of which files rsync is looking at, which includes files it skips
without actually opening:
strace --attach="$(pidof rsync)" --trace=openat
(If that's not showing anything, try removing the --trace=openat
filter and seeing if there's other syscalls with paths to filter on.)
Alternatively, this StackExchange answer suggests a way to see the currently open files including their sizes (including directories but not unchanged files being inspected):
watch lsof -p"$(pidof rsync | tr ' ' ',')"
(The same should work for a recursive cp/mv/rm.)
Similarly, for getting the status of a transfer of a single large
file, this answer attempts to read the files cp is
reading/writing to give a running percentage of how much it has copied;
a similar approach might work for rsync.