====== Ubuntu - Disk - Ramdisk - Persisting Ramdisk Data ======

A Ramdisk is a temporary storage device.

When the computer is shutdown all the data within the Ramdisk is erased.

To ensure this data is retained, the approach taken here is:

  * Save Ramdisk data to hard drive on system shutdown.
  * Load data from hard drive to Ramdisk on system boot.

<WRAP info>
**NOTE:**  The syncing from the Ramdisk to the hard disk and vice-versa will be slow, but at least the data will be stored permanently.

  * In essence, the Ramdisk acts here as a cache.

</WRAP>


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===== Create backup directory =====

Create a directory where the Ramdisk data will be saved on system shutdown:

<code bash>
sudo mkdir /mnt/ramdisk_backup
</code>

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===== Create a system service file =====

<code bash>
vi /lib/systemd/system/ramdisk-sync.service
</code>

and populate with:

<file bash /lib/systemd/system/ramdisk-sync.service>
[Unit]
Before=umount.target

[Service]
Type=oneshot
User=root
ExecStartPre=/bin/chown -Rf peter /mnt/ramdisk/
ExecStart=/usr/bin/rsync -ar /mnt/ramdisk_backup/ /mnt/ramdisk/
ExecStop=/usr/bin/rsync -ar /mnt/ramdisk/ /mnt/ramdisk_backup/
ExecStopPost=/bin/chown -Rf peter /mnt/ramdisk_backup
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
</file>

<WRAP info>
**NOTE:**  The directory where the Ramdisk is mounted and where the backup data will be saved must have the same file permissions.
</WRAP>


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===== Enable the ramdisk-sync service =====

<code bash>
sudo systemctl enable ramdisk-sync.service
</code>

<WRAP info>
**NOTE:**  The ramdisk-sync service will start automatically on system boot.
</WRAP>

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===== Reboot =====

<code bash>
sudo reboot
</code>

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===== Check whether the ramdisk-sync service is running =====

<code bash>
sudo systemctl status ramdisk-sync
</code>

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===== Check the contents of the /mnt/ramdisk and /mnt/ramdisk_backup directories =====

<code bash>
ls /mnt/ramdisk{,_backup}
</code>

<WRAP info>
**NOTE:**  Both should be empty.
</WRAP>

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===== Test =====

Copy some files to the Ramdisk /mnt/ramdisk.

Reboot again.

Check again the contents of both the /mnt/ramdisk and /mnt/ramdisk_backup directories.

  * They should be the same!

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