William Hubbs posted on Sun, 13 Oct 2013 14:32:32 -0500 as excerpted: > from what I'm seeing, we should look into converting /etc/mtab to a > symlink to /proc/self/mounts [1]. > > Are there any remaining concerns about doing this? > > If not, it seems like it would be pretty easy to make baselayout create > this symlink in the stages (I'm willing to do this work), but what about > on systems that are already installed? Should we send out a news item > and have everyone convert their /etc/mtab manually or find a way to > automate that? > > William > > [1] http://bugs.gentoo.org/show_bug.cgi?id=477498
New subthread here as I don't see this mentioned in the others (tho pacho mentions it in the bug) ... TL;DR: An /etc/mtab symlink is the generally recommended and simplest way to make a read-only root work, and I've been setup like that for some months now, so I'm all for it. =:^) Some months ago I finally upgraded my core system to SSDs, and with that, btrfs (I had been on reiserfs for years with very good results even thru hardware issues as since ordered-by-default journaling went in, anyway, it's an incredibly stable filesystem that doesn't have the kernel folks monkeying around with it and trying stuff like the infamous ext3- writeback-by-default tricks, like the ext* filesystems do, but unfortunately reiserfs simply was no designed for nor is it suited to SSDs), which of course is still an experimental filesystem, for good reason as altho the mainstream case tends to work relatively well, they're still fixing critical corner-case bugs with every kernel release. So to hopefully counter some of the additional risk, and because I had been looking at the idea for a couple years anyway, I setup a read-only root by default. And I'll tell you what, it sure is nice knowing that after a hard shutdown and reboot, while /home and /var/log will probably have integrity errors due to the bad shutdown and I'll need to do a btrfs scrub to repair them (a pair of SSDs with most filesystems in btrfs raid1 mode for both data and metadata, so there's the second copy of all (meta)data to read and restore from if the first is corrupt and fails the integrity check), root itself should be safe, since it was mounted read- only and thus no ongoing writes could have been occurring there when the crash occurred. And of course the btrfs recovery tools are on root, so if worse did come to worse, they should be fine to use in recovering /home, since the root filesystem was read-only the entire period and thus should be undamaged. =;^) Of course in ordered to setup a read-only root, I had to make some changes, including the one under discussion here, making /etc/mtab a symlink to /proc/self/mounts. (Actually, I symlinked it to /proc/mounts, but as mentioned elsewhere in the thread, on a modern kernel since mount namespaces, that's a symlink to /proc/self/mounts already, so same ultimate result.) So I'm all for the change, since that will bring the default gentoo installation one step closer to a read-only root, meaning one less thing for people who want to setup that way to have to worry about. =:^) Meanwhile, the handbook has for years suggested a separate /boot and mentioned the separate /home option. Once we have /etc/mtab as a symlink, the next logical step would be to consider upgrading that separate /home option to suggested default, adding /var/log as a suggested default, and making the default fstab options for / include ro, thus increasing default gentoo system data robustness dramatically. Of course the system-updates/portage discussion would then need a reminder to remount / rw, but with /etc/mtab a symlink, further necessary changes are minor, and it really will improve gentoo system robustness dramatically, likely saving a number of users the headache of having to recover a screwed up root, simply because it was mounted writable and didn't happen to be in a consistent state when the system crashed. (Arguably that should be a (sub-)thread of its own, thus the retitled subthread, already top-level.) -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman
