fsck-less Booting?

patrick42 asks: "I am working on a project where I'll be replacing a DOS/Windows-based system with that of Linux or FreeBSD. The company for whom I'm working uses cheap PC's running some proprietary software on DOS/Windows to perform a certain task. The machines are deployed in environments where there are no keyboards or displays, and minimum-wage clerks are the people watching these machines. The company has decided to go with a free Unix system because they no longer wish to pay the licensing fees for Windows. The machines get unplugged all the time when they are moved or whatnot. They do not get a proper shutdown procedure ever, and it's not possible to change this due to the environments in which they are deployed. I've been told that they've never had a problem running DOS in terms of filesystem corruption. So I guess I'm looking for the safest filesystem possible that I can use with either FreeBSD or Linux. My head would be served on a platter if I picked something that sometimes requires user-intervention." Note that Ask Slashdot covered a similar question back in 1999, the situations differed, but the need remains the same: can Linux work in environments where proper shutdowns are rare-to-non-existant?

"I have run many Linux machines, and I've experienced firsthand (only on occassion) where a machine did not get properly shutdown, and then on the next boot user-interaction was required to run fsck manually.

I really want to use either FreeBSD or Linux, but if there is any chance of this happening (hardware failures excluded) where someone needs to manually run fsck, I will not be able to use them.

I've been reading about the ext3 filesystem, and how corruption is quite rare, but it still seems possible. UFS claims to be quite stable as well, but fsck-less booting will not be available until FreeBSD 5.0 (from what I've read).

These machines aren't doing too much writing to the disk -- they are mostly just reading data, but that isn't to say that there will be no disk writes at all.

Can anyone offer some advice?"

Comments

Synchronous

[Phaid]

I've had to deal with a situation like this before - a hard drive in a laser printer, where there was no shutdown procedure, only an on/off switch. I used the "sync" option - e.g.

mount -t ext2 -o sync /dev/hda2 /usr

This causes the filesystem to be mounted synchronous, so that there are no deferred writes and all disk writes are committed to the disk before the I/O call returns.

This is not 100% fool proof either, as it is still possible to power down the machine in the middle of a write, but it makes it much more difficult to screw up.

Re:Synchronous

[reynaert]

Be wary of modern hard drives---some of them may use a write cache internally (from what I have heard, anyway).

You can disable this with hdparm -W 0 /dev/hd*. Other hdparm parameters may also be interesting.

Diskless?

[Col. Klink (retired)]

Are the machines networked? You could use Etherboot to boot over the network and have no local disks (or just a floppy if you don't want to make boot EPROMs).

You didn't really say much about what the "certain task" these machines do. Do they need to save a lot of data? You could boot off a CD-ROM and use RAM disks for /var and other writeable partitions. Each time the machine is unplugged, it returns entirely to its initial state.

If you want to save a small amount of data, you could put a VFAT formatted floppy and write persistent data there.