Re: git: 36db6b04962a - main - hier(7): document /home/ and /usr/home/

On 10 May 2023, at 10:13, Cy Schubert wrote:

> In message <ba22a75d-06c0-371e-603e-7ded9d1dca97@freebsd.org>, Mitchell
> Horne w
> rites:
>> On 5/10/23 11:19, Rodney W. Grimes wrote:
>>>> The branch main has been updated by mhorne:
>>>>
>>>> URL: https://cgit.FreeBSD.org/src/commit/?id=36db6b04962a01ff7b21592def02d
>> 4c570dac939
>>>>
>>>> commit 36db6b04962a01ff7b21592def02d4c570dac939
>>>> Author:     Mitchell Horne <mhorne@FreeBSD.org>
>>>> AuthorDate: 2023-05-10 12:53:56 +0000
>>>> Commit:     Mitchell Horne <mhorne@FreeBSD.org>
>>>> CommitDate: 2023-05-10 13:25:17 +0000
>>>>
>>>>      hier(7): document /home/ and /usr/home/
>>>>
>>>>      Reviewed by:    imp
>>>>      MFC after:      1 week
>>>>      Sponsored by:   The FreeBSD Foundation
>>>>      Differential Revision:  https://reviews.freebsd.org/D40002
>>>> ---
>>>>   share/man/man7/hier.7 | 10 ++++++++++
>>>>   1 file changed, 10 insertions(+)
>>>>
>>>> diff --git a/share/man/man7/hier.7 b/share/man/man7/hier.7
>>>> index ff11289436a1..b6759dd6e65b 100644
>>>> --- a/share/man/man7/hier.7
>>>> +++ b/share/man/man7/hier.7
>>>> @@ -90,6 +90,10 @@ file descriptor files;
>>>>   see
>>>>   .Xr \&fd 4
>>>>   .El
>>>> +.It Pa /home/
>>>> +user HOME directories.
>>>> +This is a symlink to
>>>> +.Pa /usr/home/
>>>
>>> /usr is "contains the majority of user utilities and applications"
>>> it should not contain home directories.
>>>> I do not know when this move to usr came about it was traditionally
>> /home.
>>> I do not know why /usr/home even exists, it is not needed by
>>> anything I am aware of.  If we have a compatible link it
>>> should be, usr/home -> ../home and /home should be the
>>> directory.
>>>
>>
>> I agree that /usr/home is strange, and is unique (?) to FreeBSD.
>>
>> The oldest commit in the output of `git log --grep '/usr/home'` is:
>>
>> commit f2400d465896a8e4f6fdc57eba840cf49b25bbbd
>> Author: David Nugent <davidn@FreeBSD.org>
>> Date:   Fri Jan 3 04:42:18 1997 +0000
>>
>>      Implemented /home -> /usr/home symlink kludge.
>>      If home basedir would be created in the root partition, create
>>      it under /usr instead, and symlink /basedir -> /usr/basedir.
>>
>> Notes:
>>      svn path=/head/; revision=21242
>>
>>
>> So it has been this way for 26 years at least. I do not know what to say
>> about whether /usr "should" contain it, but it does.
>
> Usually history matters. I can understand not changing it. On the flip
> side, I cut my UNIX teeth on SunOS 4 and Solaris where /home was /home --
> albeit automounted from /export/home on localhost or some NFS server. In
> the Red Hat land at $JOB, /home is its own partition (actually an LVM
> volume). In both cases /home is not in /usr because end-users can fill
> /usr. This can be problematic operationally because it's yet another
> headache to deal with should someone fill the filesystem. Filling /usr is
> more serious than filling /home.
>
> As a point of interest, when I installed my first FreeBSD many moons ago I
> used the Solaris standard of /export/home, using amd (now automount) to
> serve my /home. I'm not advocating we do this, it's overkill, but /home
> should not live in /usr. It's a potential headache for any sysadmin.
>
> With ZFS the solution is easy. With UFS based systems there are a lot of
> other factors that go into how we install the "default" from the get-go.

The situation is a fair mess.  It took me a little while to figure out that
the kludge referenced above is in the pw(8) command, which is used as the
backend to adduser(8).  Neither /home nor /usr/home is in the base package.
adduser defaults to /home/user, and creates the parent directory (e.g. /home)
if it does not exist, but if there is no internal slash, pw moves the parent
to /usr.  In this case, it makes the symlink from  root.  zfs is different,
in that it includes a usr/home dataset already (created by bsdinstall).
In this case, creating a user with /home/user causes the symlink to be added
as a side effect.

I’m sure the kludge was originally done when root and /usr were separate
file systems by default, root was small, and there was no /home by default.
However, we now default to a single large file system (with datasets, in
the zfs case).

All of this really is a horrible kludge, and it is a house of cards.  I’m
amazed that it doesn’t break more often.  I’m tempted to remove the kludge
and change the zfs setup to create a home dataset rather than usr/home.
However, if zfs users explicitly configure a home directory under /usr/home,
this would end up in the usr dataset.  An alternative would be to remove the
code from pw to create the parent directory entirely (which seems sensible),
and create a /home directory for ufs installs.  I don’t know how well known
it is that adduser/pw will create parent directories for home directories
though.  This cleanup would change the default location for home directories
to /home, which makes more sense.  It would require documentation, e.g. in
the release notes.  The changes would only affect new installations, not
upgrades.

Thoughts?

		Mike