Netapp's "snaplock" technology allows one to create "write-once, read many" ("WORM") volumes that allow data to be written but not modified or deleted -- especially not if "compliance" mode is used. While this is not a true "WORM" -- it's still done entirely in software and therefore can theoretically be hacked -- it adds an extra layer of security to your infrastructure, especially if you already rely on netapps for your NAS needs.
Any file stored on a snaplock volume can be given WORM protection by first doing a "touch" and setting the atime with the date in the future, and then setting a read-only mode on the file. If after setting "read-only" on a file you give it a read-write permission, the file will be put into "append" mode -- data can be appended to the file, but no previously stored data can be modified or deleted (data is "locked" in 256K chunks).
This is extremely handy for storing system logs or copies of emails for archival purposes. We have a syslog aggregator that receives all our system logs, including auditd. I wrote a simple script that runs out of /etc/cron.daily that pre-creates the "append-only" locations for rsyslog to write to, plus sets read-only on yesterday's logs. Here's the code:
On rsyslog's side of things you'll need something like the following in order to write to these locations:
And, finally, you'll need to do some SELinux manipulations in order to allow rsyslog to write to the NFS location, such as setting the mount context to var_log_t. If you do that, then you'll need the following SELinux policy in order to allow the cron script from above to run: