Space requirements for initramfs [LWN.net]

Space requirements for initramfs

Posted Jan 28, 2012 12:39 UTC (Sat) by gbrun (guest, #82611)
Parent article: The case for the /usr merge

While it is certainly true that the "big" desktop distros are all based on initramfs/initrd "preboot" environments, this does not mean it is an equally well-suited solution for all Linux installations.

Obviously, in situations where the initramfs approach works, the traditional roles of /bin, /sbin and /lib as a "rescue system" are no longer required.

On the other hand, the initramfs approach requires a rather large amount of main memory in order to store the extracted contents of the preboot environment.

This is certainly not a problem for the current generation of hardware where most boxes have at least 1 gig of RAM.

But there are still a lot of smaller and more restricted older systems out there with as little as 16 megs of RAM!

Those systems can still run a (somewhat stripped-down) Linux installation (typically 2.4 or 2.5 based), but they certainly cannot afford to extract and run an initramfs.

Such systems *depend* on the traditional /bin /sbin /lib layout for a rescue system, especially in cases where alternative boot devices are not available.

Merging /usr/bin and /bin is therefore certainly a valid choice for bloated desktop distros, but I strongly advise against general adoption of this scheme in a forthcoming update of the FHS.

What *could* be adopted, though, is the *optional* of replacement /bin, /sbin and /lib with symlinks.

Space requirements for initramfs

Posted Jan 28, 2012 14:19 UTC (Sat) by HelloWorld (guest, #56129) [Link] (2 responses)

Why would you ever need a "rescue system" on an embedded system? There's typically not much to rescue there, and things can be fixed by simply flashing a new firmware.

Space requirements for initramfs

Posted Jan 28, 2012 14:35 UTC (Sat) by bluss (guest, #47454) [Link] (1 responses)

Maybe it's an exploration robot on a different planet?

Space requirements for initramfs

Posted Jan 28, 2012 15:53 UTC (Sat) by Eckhart (guest, #74500) [Link]

> Maybe it's an exploration robot on a different planet?

Bonus points for picking the most unlikely scenario?

Space requirements for initramfs

Posted Jan 28, 2012 14:54 UTC (Sat) by Los__D (guest, #15263) [Link]

In what way does desktop distributions and services relate to 16MB devices?

If you are using a small embedded device, you would of course use a distribution for embedded purposes, or roll it yourself, making all of this moot.

Space requirements for initramfs

Posted Jan 29, 2012 0:40 UTC (Sun) by dlang (guest, #313) [Link]

don't forget virtualized systems, the main system may have lots of ram, but how many virtual machines do you want to run on that hardware?

Space requirements for initramfs

Posted Jan 30, 2012 0:20 UTC (Mon) by mezcalero (subscriber, #45103) [Link]

On embedded machines it's usually not interesting to split off /usr anyway. And systems without /usr split off can boot without initrd just fine.

Note that the same people who are behind the /usr merge have actually been working on making Linux work with a read-only / out-of-the-box, for use in embedded and stateless systems (We are mostly there, but not entirely). We have the embedded use of Linux and systemd firmly on our map, but initrd-less systems with /usr split off are definitely of little usefulness in our eyes, since they are useless for embedded and pointless on bigger setups.