Editing Knoppix (section)

== Saving changes in the environment ==
Prior to Knoppix 3.8.2, any documents or settings a user created would disappear upon reboot. This lack of persistence then made it necessary to save documents directly to a hard drive partition, over the network, or to some [[removable media]], such as a USB flash drive.

It was also possible to set up a "persistent home directory", where any documents or settings written to the user's home directory would automatically be redirected to a hard drive or removable media, which could be automatically [[Mount point|mounted]] on bootup. A single file, ''knoppix.img'', was cached on the rewritable media and used to simulate a file system into which files were written for later use. This allowed the user to transparently write to their home directory.

[[Union mount]] support was added in version 3.8.1 through [[UnionFS]]. This was later replaced by [[Aufs]] in 5.1.0 to improve stability.<ref>{{cite web|url=http://knopper.net/knoppix/knoppix51-en.html|title=KNOPPIX 5.1 - Live Linux Filesystem On CD|access-date=26 May 2015|url-status=live|archive-url=https://web.archive.org/web/20150511123911/http://knopper.net/knoppix/knoppix51-en.html|archive-date=11 May 2015}}</ref> The union mount allowed virtual updates to the data on the read-only CD/DVD media by storing changes on separate writable media and then representing the combination of the two as single [[Computer data storage|storage device]]. The writable media could be memory ([[ramdisk]]), a hard disk, USB flash drive, etc. This means that the user could modify the software installed on the Knoppix system, such as by using [[Advanced Packaging Tool|APT]] to install or update software. The storage device containing the changes needed to be present whenever Knoppix is started, else only the original data from the disc would be used. While Knoppix would scan available storage devices for a persistent home directory by default, a user could dictate a specific location with a boot option ([[#Boot options|see below]]) such as:

<code>home=/dev/hda1/knoppix.img</code><ref name="Cheat codes">{{cite web|url=http://knoppix.net/wiki/Cheat_Codes|title=Cheat Codes|access-date=26 May 2015|url-status=live|archive-url=https://web.archive.org/web/20150627173504/http://knoppix.net/wiki/Cheat_Codes|archive-date=27 June 2015}}</ref>

By carrying a Knoppix CD and a USB flash drive, a user could have the same environment, programs, settings, and data available on any computer that could run Knoppix.

This functionality was only available through Knoppix 5.1.1 (CD release) or 5.3.1 (DVD release). Subsequently, the Live CD paradigm has transformed into portable operating systems that run on external storage.