The messages which are printed to stdout by rsync are directed to a log file by rsnapshot.

The name of the log file follows the entry logfile in the config file for the backup job.

It defaults to /var/log/rsnapshot-backup/<systemname>/log which is renamed to /var/log/rsnapshot-backup/<systemname>/log-<YYYYmmdd-HHMMSS> after the backup job is completed.

Unfortunately, rsnapshot lets escape rsync's stderr messages without recording them. So they would end up on your terminal or most likely are cought by cron and sent per email.

Rsnapshot-backup intercepts rsnapshot's stderr and redirects the message to a file which name is derived from the logfile entry in the config file for the backup job.

It defaults to /var/log/rsnapshot-backup/<systemname>/log-error which is renamed to /var/log/rsnapshot-backup/<systemname>/log-error-<YYYYmmdd-HHMMSS> after the backup job is completed.

The -error part of the file name is not configurable.

If there is no output on stderr there will be no log-error-* file.

The time stamps in the file names are identical for log-* and log-error-* so the two corresponding log files can be matched easily.

mkdir /root/tmp
cd    /root/tmp
while sleep 0.05 ; do  ( F=$( mktemp xxx-$( date -Is )-XXXXXX ) ; date > $F; sleep 0.2 ; rm $F ) & done

This creates 20 files per second which are removed after 200ms.

The error provoked would be something like:

------ BACKUP OF '/etc/rsnapshot-backup.d/enabled/conf.vstest01' ------
file has vanished: "/root/tmp/xxx-2017-06-27T14:13:50+0000-STgDmA"
rsync warning: some files vanished before they could be transferred (code 24) at main.c(1655) [generator=3.1.1]
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