Files not listed in backup image

[X2]

I think this is quite a basic question but wanted general input also.

One of our sys admins requested a restore of files in a folder (on RHEL 6.9 client/Standard backup). I back it up daily (1 full/month, diff daily). The folder in question was backed up on 24th April 2018 along with other folders along with it (during a DIFF backup). However, there were no files that were backed up from that folder (a few JPG image files). Other folders at same path had files from 24th and they were backed up.

The JPG image files in the folder in question show last modified date from 18th April 2018. As the backup which runs daily, was a DIFF, it looked for files changed since the last DIFF and the JPG files in that folder did not fall under that criterion and were not backed up. Is this correct explanation or am I missing something?

PS: files could have been put there via rsync using archive flag, user didn't give details.

[Matthias_Meier]

from my point of view, you are correct. I also ran into this in the past. And this is one of the disadvantages when using time stamps with incremental or diffential backups - which is the only option on Linux/UNIX. If the software, that puts the file on the filesystem is not changing the last modified date, for instance sync software, then this issue appears. Only a new full will cover these files - else, you copy these files again to another folder, which is setting a new (the current) last modified date.

Greetings, Matthias

[X2]

For anyone who comes looking at this thread in future: yes, modified time older than last DIFF will not make the file get backed up during subsequent DIFF backups.

I was able to reproduce the situation on my test backup domain. I rsync'd an old file and NetBackup didn't back it up even though it was in a newly created folder.

[Marianne]

NBU uses mtime by default for Incr backups.

You may want to use ctime instead.

See this extract from NBU Admin Guide: 

How NetBackup determines when UNIX files are due for backup

https://www.veritas.com/support/en_US/doc/18716246-126559472-0/v41780104-126559472

When a file is moved from one location to another, the ctime of the file changes, but the mtime remains unchanged. If NetBackup uses only the mtime to determine the files that are due during an incremental backup, it does not detect these moved files. For sites where using the mtime might create a problem, use the ctime to determine files due to be included in an incremental backup. The ctime is used if the bp.conf file contains the USE_CTIME_FOR_INCREMENTALS and DO_NOT_RESET_FILE_ACCESS_TIME entries.