journaled filesystems
srm is a command-line program to delete files securely.
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Of course srm can delete files on any file system supported by your kernel. It uses normal routines to overwrite the data.
Of course your real question is, if the data really reaches the hard disk with those multiple passes when using a journaled file system. An intelligent journalling file system might notice that the pending data writes could be omitted because the file was just deleted and thus skip those write operations.
Currently srm disables journalling of the file's data for ext3 file systems. I can't tell if it really works as advertised. All of this is still work in progress and some improvements are schedules for future releases.
The default filesystem in CentOS 7 is XFS (also a journal file system)
In my experience, the only way to keep sensitive data off the drive is to encrypt it and/or use tmpfs with encrypted swap. (tmpfs is swap backed, thus defeating the purpose of a ram disk for sensitive data)