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Can I have separate / and /tmp but /home + /var on one partition somehow?

Separate /tmp is good because I can set it up with some quick unreliable filesystem. I often change distributions therefore separate / is a blessing - quick re-install and I'm good as long as /home and /var are untouched.

The problem is, I don't want to designate space for any of the last three - I want them to share available resources. I sometimes need more space in /var and I can see there's available space in /home that I cannot use, sometimes it's the other way around. It's frustrating. Any ideas?

  • You don't separate / and /usr anymore. You can't do reinstalls leaving /usr untouched either (and /var not completely). – frostschutz Oct 19 '16 at 11:37
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    Why? Any sources on that? What is a good practice regarding partitions separation then? – cprn Oct 19 '16 at 11:45
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    @Cyprian, freedesktop.org/wiki/Software/systemd/separate-usr-is-broken (it's by the systemd folks but not directly related to it) – ilkkachu Oct 19 '16 at 20:55
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You can always mount your third partition somewhere (like /mnt/combo or something), and then bind-mount subdirectories from this mountpoint to the three designated directories.

In fstab, this would look something like

UUID=... /mnt/combo        auto    defaults
/mnt/combo/usr /home        none    bind
/mnt/combo/var /var        none    bind
/mnt/combo/home /home        none    bind

Also consider this: /home makes sense to live on a separate partition - even better, a separate drive, which can be somehow protected (raid, backups,...). /var would make sense to be separate if you really have something personal in there (websites and such), otherwise it makes no difference. /usr can definitely be part of /, it makes no sense to have it separate because on a modern system, the distinction between /bin and /usr/bin is blurred and noone cares about it anymore, and segmenting a system only creates problems if one of the partitions somehow doesn't mount.

/tmp should normally be ram-backed anyway (tmpfs), unless you really are running out of RAM, and most distros do that by default unless you change it.

Big picture: separate /home if you have to, the rest is just overhead - you probably have no reason to have different filesystem types or different permissions on any of these, and partitioning doesn't usually mean physical separation (same hard drive?).

  • How would that work during reinstall? Each time I reinstall it would write to /home, /usr, /var on root partition and afterwards I would manually "replace" mountpoints with /home, /usr and /var from my /mnt/combo? – cprn Oct 19 '16 at 11:47
  • Yes, that would work, if that's what you want. But then, what does a reinstall even do? You usually want to keep configuration, so keeping /etc/ is more important than the rest, and there isn't much outside /usr anyway on a fresh install (/boot and that's it). If you want the install to write to these partitions, you'll simply have to mount this before running installation. – orion Oct 19 '16 at 11:50
  • @CyprianGuerra take a look into kickstart files. They automate tasks during installation. If you're worried about the configuration disappearing between installs a kickstart can help you out. – Centimane Oct 19 '16 at 12:22
  • Okay, I'm marking this as a valid answer because it resolves my question... I have to re-think my idea of reinstall, though, but this is a separate issue. And no, I don't think I want to keep configs because I use reinstall as the last resort when I'm lost trying to fix whatever I broke and need a working system ASAP, default configs, default packages. – cprn Oct 19 '16 at 15:56
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    In that case, in my opinion, it's better to wipe clean the /usr too. Because package repositories change. Things get updated. Very likely, old applications wouldn't work with fresh install. I would strongly recommend to just have a list of packages you want... and write a script that would quickly install everything, always the same things - and maybe simulatenously fix the things you want personalized (hostname, network config,...). A simple shell script that does the full system install. Otherwise you'll spend hours debugging when compatibility breaks. – orion Oct 19 '16 at 16:04

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