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- The key to understanding how Puppy works is the initial boot script,
- /initrd/init.
- In a nutshell, everything you see in /initrd is the "initial ramdisk",
- which is actually /dev/ram0. For Puppy 4.0 and later, the kernel uses a slightly
- different technique and it is more correct to call it the "initramfs" and
- /dev/ram0 is not used.
- With Puppy prior to 4.0, the initial ramdisk is not discarded after bootup.
- From 4.0 onward, the initramfs is discarded, but much of it is transfered to
- the main filesystem in the /initrd directory. Technically different, but
- similar end result from the users point of view.
- The directories pup_rw, pup_ro1, etc are mounted on "/" when Puppy is running.
- The number of them mounted is variable, at least pup_rw will be.
- The usual situation is pup_rw, pup_ro1 and pup_ro2 are mounted on "/".
- When control transfers from the initial ramdisk or initramfs to the main filesystem,
- these mount-points are relocated to inside /initrd.
- /initrd/pup_rw
- This is the writable folder. Usually it is tmpfs (temporary filesystem) in ram.
- However, a personal storage file (named "pup_save.2fs" or similar) or partition
- could be mounted directly on here (in which case it won't be on /initrd/pup_ro1).
- /initrd/pup_ro1
- This is usually your saved files, and the contents of pup_rw get saved to here,
- periodically or at end of session. In other words, your personal storage file or
- partition is mounted here, except see above note.
- Note that this is mounted rw, although unionfs makes it behave as ro on "/".
- /initrd/pup_ro2
- These are all the Puppy files. Normally we don't write to this, we keep it pristine.
- This file is named something like "pup-430.sfs" or similar, where the "410" is the
- 3-digit version number.
- /initrd/pup_ro3
- Recent versions of Puppy built with the Woof build system, in 2009 or later, may
- have a "zdrv" mounted on here. This is a situation in which the kernel modules and
- firmware are in a separate file named "zp430nnn.sfs" or similar (the essential
- feature to recognise this file is it starts with letter "z" and has the version
- number in it).
- unionfs
- Mounts the directories in this order:
- pup_rw
- pup_ro1
- pup_ro2
- pup_ro3
- pup_ro4
- pup_ro5
- etc.
- Where the higher directory has precedence. For example if files of the same name
- exist in pup_rw and pup_ro1, the file in pup_rw is the one that is "seen".
- ------------------
- Barry Kauler 2009.
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