Re: merged /usr considered harmful (was Re: Bits from the Technical Committee)
On Sun, 18 Jul 2021 16:21:24 -0700, Russ Allbery <rra@debian.org>
wrote:
>I agree with the other feedback that you are overpartitioning your disk.
It is especially evident in the df output where there are two-digit
amounts of gigabytes free on most of those HUGE partitions.
>I used to do this back when I was first learning UNIX in the 1990s because
>it seems like a good idea and it does isolate one part of the system from
>another if it uses an excessive amount of space. But what I found in
>practice, and what almost everyone who does this eventually finds in
>practice, is that this much partitioning drastically reduces the long-term
>flexibility of the system. It requires you predict in advance what parts
>of the system will grow, and when you guess wrong, you end up with
>symlinks trying to move directories from a partition with no free space to
>another partition with free space, with all the complexity and breakage
>that can cause.
Nowadays, with LVM, file systems can easily grow, even online. I have
stopped putting /usr on a dedicated file system as the usrmerge began
to show up on the horizon, but I still use dedicated file systems for
/home and /var.
I am NOT looking forward having to manually convert legacy systems to
merged /usr and I do sincerely hope that Debian will choose a way to
get away without throwing away systems that have just a small /, still
supporting a dedicated /usr as long as it's mounted by initramfs. I am
not sure whether we ever issued a clear statement about that.
>There are some technical reasons to separate /boot if you are using a file
>system for other partitions that isn't suitable for early boot (or if
>you're using cryptsetup or other file system layers). /boot/efi is always
>a separate partition because of how it works. Apart from those two
>special cases, the only reason to put something on a separate file system
>is if you have a clear and compelling reason why you expect a given file
>system to run out of space and you want to ensure that it cannot take
>space from other parts of the system.
I also believe that smaller file systems are unlikely to break and
that a system that can boot up to a ssh-able state even with a broken
file system is way easier to fix. We have taken a huge step back in
that regard with systemd since the systemd rescue mode requiring the
"real" root password even for minor startup failures is way more
unfriendly than what we had before. Many installations closely guard
the root password for real emergencies (I have been working on big
installations for years and have NEVER seena case where the "real"
root password was actually used - it is usually easier to rebuild
affected systems from scratch).
>This can be a good justification for putting /home on a separate partition
>*if* you are running a multi-user system. But otherwise, separating out
>things like /var or /usr/local or /opt or /srv is more likely to cause you
>long-term headaches than it is to do anything useful.
I disagree for /var (maybe just for /var/log or parts of /var/lib).
Greetings
Marc
--
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Marc Haber | " Questions are the | Mailadresse im Header
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