This section is loaded in a bunch of places, so this affects many
man pages.
1. point the reader to the synopsis section, which has the exact paths
that are used to load files.
2. put the "reference" part first, and recommendations later, in separate
paragraphs.
3. describe how individual settings and whole files are replaces.
Closes#12791.
This extends on d253a45e1c, and instead of
merging just a single flag from previous mount entries of
/proc/self/mountinfo for the same path we merge all three.
This shouldn't change behaviour, but I think make things more readable.
Previously we'd set MOUNT_PROC_IS_MOUNTED unconditionally, we still do.
Previously we'd inherit MOUNT_PROC_JUST_MOUNTED from a previous entry on
the same line, we still do.
MOUNT_PROC_JUST_CHANGED should generally stay set too. Why that? If we
have two mount entries on the same mount point we'd first process one
and then the other, and the almost certainly different mount parameters
of the two would mean we'd set MOUNT_PROC_JUST_CHANGED for the second.
And with this we'll definitely do that still.
This also adds a comment explaining the situation a bit, and why we get
into this situation.
(This also changes the suggested /etc/nsswitch.conf line to use for
hooking up nss-system to use glibc's [SUCCESS=merge] feature so that we
can properly merge group membership lists).
This also updates the suggested PAM snippet in a number of way:
1. Be closer to the logic nowadays implemented in Fedora where the
auth/account/password stacks are all finished off with
pam_{deny|permit}.so
2. Make pam_unix.so just "sufficient" instead of "required" (paving
ground for pam_systemd_home.so being hooked in as additional
sufficient module.
3. Only do pam_nologin in the "account" stack, since it's about account
validity really.
4. Use modern parameters to pam_unix when changing passwords, i.e.
sha512 and shadow, and use already set up passwords (preparing ground
for pam_systemd_home again)
This changes nss-systemd to use the new varlink user/group APIs for
looking up everything.
(This also changes the factory /etc/nsswitch.conf line to use for
hooking up nss-system to use glibc's [SUCCESS=merge] feature so that we
can properly merge group membership lists).
Fixes: #12492
