docs: use collections to structure the data

1 files changed, 0 insertions, 170 deletions

diff --git a/docs/USER_NAMES.md b/docs/USER_NAMES.md
deleted file mode 100644
index 74c24b5157..0000000000
--- a/docs/USER_NAMES.md
+++ /dev/null
@@ -1,170 +0,0 @@
----
-title: User/Group Name Syntax
-category: Users, Groups and Home Directories
-layout: default
-SPDX-License-Identifier: LGPL-2.1-or-later
----
-
-# User/Group Name Syntax
-
-The precise set of allowed user and group names on Linux systems is weakly
-defined. Depending on the distribution a different set of requirements and
-restrictions on the syntax of user/group names are enforced — on some
-distributions the accepted syntax is even configurable by the administrator. In
-the interest of interoperability systemd enforces different rules when
-processing users/group defined by other subsystems and when defining users/groups
-itself, following the principle of "Be conservative in what you send, be
-liberal in what you accept". Also in the interest of interoperability systemd
-will enforce the same rules everywhere and not make them configurable or
-distribution dependent. The precise rules are described below.
-
-Generally, the same rules apply for user as for group names.
-
-## Other Systems
-
-* On POSIX the set of [valid user
-  names](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_437)
-  is defined as [lower and upper case ASCII letters, digits, period,
-  underscore, and
-  hyphen](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_282),
-  with the restriction that hyphen is not allowed as first character of the
-  user name. Interestingly no size limit is declared, i.e. in neither
-  direction, meaning that strictly speaking, according to POSIX, both the empty
-  string is a valid user name as well as a string of gigabytes in length.
-
-* Debian/Ubuntu based systems enforce the regular expression
-  `^[a-z][-a-z0-9]*$`, i.e. only lower case ASCII letters, digits and
-  hyphens. As first character only lowercase ASCII letters are allowed. This
-  regular expression is configurable by the administrator at runtime
-  though. This rule enforces a minimum length of one character but no maximum
-  length.
-
-* Upstream shadow-utils enforces the regular expression
-  `^[a-z_][a-z0-9_-]*[$]$`, i.e. is similar to the Debian/Ubuntu rule, but
-  allows underscores and hyphens, but the latter not as first character. Also,
-  an optional trailing dollar character is permitted.
-
-* Fedora/Red Hat based systems enforce the regular expression of
-  `^[a-zA-Z0-9_.][a-zA-Z0-9_.-]{0,30}[a-zA-Z0-9_.$-]?$`, i.e. a size limit of
-  32 characters, with upper and lower case letters, digits, underscores,
-  hyphens and periods. No hyphen as first character though, and the last
-  character may be a dollar character. On top of that, `.` and `..` are not
-  allowed as user/group names.
-
-* sssd is known to generate user names with embedded `@` and white-space
-  characters, as well as non-ASCII (i.e. UTF-8) user/group names.
-
-* winbindd is known to generate user/group names with embedded `\` and
-  white-space characters, as well as non-ASCII (i.e. UTF-8) user/group names.
-
-Other operating systems enforce different rules; in this documentation we'll
-focus on Linux systems only however, hence those are out of scope. That said,
-software like Samba is frequently deployed on Linux for providing compatibility
-with Windows systems; on such systems it might be wise to stick to user/group
-names also valid according to Windows rules.
-
-## Rules systemd enforces
-
-Distilled from the above, below are the rules systemd enforces on user/group
-names. An additional, common rule between both modes listed below is that empty
-strings are not valid user/group names.
-
-Philosophically, the strict mode described below enforces an allow list of
-what's allowed and prohibits everything else, while the relaxed mode described
-below implements a deny list of what's not allowed and permits everything else.
-
-### Strict mode
-
-Strict user/group name syntax is enforced whenever a systemd component is used
-to register a user or group in the system, for example a system user/group
-using
-[`systemd-sysusers.service`](https://www.freedesktop.org/software/systemd/man/systemd-sysusers.html)
-or a regular user with
-[`systemd-homed.service`](https://www.freedesktop.org/software/systemd/man/systemd-homed.html).
-
-In strict mode, only uppercase and lowercase characters are allowed, as well as
-digits, underscores and hyphens. The first character may not be a digit or
-hyphen. A size limit is enforced: the minimum of `sysconf(_SC_LOGIN_NAME_MAX)`
-(typically 256 on Linux; rationale: this is how POSIX suggests to detect the
-limit), `UT_NAMESIZE-1` (typically 31 on Linux; rationale: names longer than
-this cannot correctly appear in `utmp`/`wtmp` and create ambiguity with login
-accounting) and `NAME_MAX` (255 on Linux; rationale: user names typically
-appear in directory names, i.e. the home directory), thus MIN(256, 31, 255) =
-31.
-
-Note that these rules are both more strict and more relaxed than all of the
-rules enforced by other systems listed above. A user/group name conforming to
-systemd's strict rules will not necessarily pass a test by the rules enforced
-by these other subsystems.
-
-Written as regular expression the above is: `^[a-zA-Z_][a-zA-Z0-9_-]{0,30}$`
-
-### Relaxed mode
-
-Relaxed user/group name syntax is enforced whenever a systemd component accepts
-and makes use of user/group names registered by other (non-systemd)
-components of the system, for example in
-[`systemd-logind.service`](https://www.freedesktop.org/software/systemd/man/systemd-logind.html).
-
-Relaxed syntax is also enforced by the `User=` setting in service unit files,
-i.e. for system services used for running services. Since these users may be
-registered by a variety of tools relaxed mode is used, but since the primary
-purpose of these users is to run a system service and thus a job for systemd a
-warning is shown if the specified user name does not qualify by the strict
-rules above.
-
-* No embedded NUL bytes (rationale: handling in C must be possible and
-  straightforward)
-
-* No names consisting fully of digits (rationale: avoid confusion with numeric
-  UID/GID specifications)
-
-* Similar, no names consisting of an initial hyphen and otherwise entirely made
-  up of digits (rationale: avoid confusion with negative, numeric UID/GID
-  specifications, e.g. `-1`)
-
-* No strings that do not qualify as valid UTF-8 (rationale: we want to be able
-  to embed these strings in JSON, with permits only valid UTF-8 in its strings;
-  user names using other character sets, such as JIS/Shift-JIS will cause
-  validation errors)
-
-* No control characters (i.e. characters in ASCII range 1…31; rationale: they
-  tend to have special meaning when output on a terminal in other contexts,
-  moreover the newline character — as a specific control character — is used as
-  record separator in `/etc/passwd`, and hence it's crucial to avoid
-  ambiguities here)
-
-* No colon characters (rationale: it is used as field separator in `/etc/passwd`)
-
-* The two strings `.` and `..` are not permitted, as these have special meaning
-  in file system paths, and user names are frequently included in file system
-  paths, in particular for the purpose of home directories.
-
-* Similar, no slashes, as these have special meaning in file system paths
-
-* No leading or trailing white-space is permitted; and hence no user/group names
-  consisting of white-space only either (rationale: this typically indicates
-  parsing errors, and creates confusion since not visible on screen)
-
-Note that these relaxed rules are implied by the strict rules above, i.e. all
-user/group names accepted by the strict rules are also accepted by the relaxed
-rules, but not vice versa.
-
-Note that this relaxed mode does not refuse a couple of very questionable
-syntaxes. For example, it permits a leading or embedded period. A leading period
-is problematic because the matching home directory would typically be hidden
-from the user's/administrator's view. An embedded period is problematic since
-it creates ambiguity in traditional `chown` syntax (which is still accepted
-today) that uses it to separate user and group names in the command's
-parameter: without consulting the user/group databases it is not possible to
-determine if a `chown` invocation would change just the owning user or both the
-owning user and group. It also allows embedding `@` (which is confusing to
-MTAs).
-
-## Common Core
-
-Combining all rules listed above, user/group names that shall be considered
-valid in all systemd contexts and on all Linux systems should match the
-following regular expression (at least according to our understanding):
-
-`^[a-z][a-z0-9-]{0,30}$`