docs: Improve HOME_DIRECTORY.md

adrian5 · yuwata · commit fa16642f4a35 · 2022-02-08T21:06:53.000+09:00
diff --git a/docs/HOME_DIRECTORY.md b/docs/HOME_DIRECTORY.md
@@ -9,11 +9,11 @@ SPDX-License-Identifier: LGPL-2.1-or-later
 
 [`systemd-homed.service(8)`](https://www.freedesktop.org/software/systemd/man/systemd-homed.service.html)
 manages home directories of regular ("human") users. Each directory it manages
-encapsulates both the data store and the user record of the user so that it
+encapsulates both the data store and the user record of the user, so that it
 comprehensively describes the user account, and is thus naturally portable
 between systems without any further, external metadata. This document describes
-the format used by these home directories, in context of the storage mechanism
-used.
+the format used by these home directories, in the context of the storage
+mechanism used.
 
 ## General Structure
 
@@ -22,7 +22,7 @@ user record of the user. It follows the format defined in [`JSON User
 Records`](https://systemd.io/USER_RECORD). It is recommended to bring the
 record into 'normalized' form (i.e. all objects should contain their fields
 sorted alphabetically by their key) before storing it there, though this is not
-required nor enforced. Since the user record is cryptographically signed the
+required nor enforced. Since the user record is cryptographically signed, the
 user cannot make modifications to the file on their own (at least not without
 corrupting it, or knowing the private key used for signing the record). Note
 that user records are stored here without their `binding`, `status` and
@@ -35,13 +35,13 @@ If the plain directory or `btrfs` subvolume storage mechanism of
 `systemd-homed` is used (i.e. `--storage=directory` or `--storage=subvolume` on
 the
 [`homectl(1)`](https://www.freedesktop.org/software/systemd/man/homectl.html)
-command line) the home directory requires no special set-up besides including
+command line) the home directory requires no special setup besides including
 the user record in the `~/.identity` file.
 
 It is recommended to name home directories managed this way by
 `systemd-homed.service` by the user name, suffixed with `.homedir` (example:
 `lennart.homedir` for a user `lennart`) but this is not enforced. When the user
-is logged in the directory is generally mounted to `/home/$USER` (in our
+is logged in, the directory is generally mounted to `/home/$USER` (in our
 example: `/home/lennart`), thus dropping the suffix while the home directory is
 active. `systemd-homed` will automatically discover home directories named this
 way in `/home/*.homedir` and synthesize NSS user records for them as they show
@@ -54,19 +54,19 @@ mechanism, except that the home directory is encrypted using `fscrypt`. (Use
 `--storage=fscrypt` on the `homectl` command line.) Key management is
 implemented via extended attributes on the directory itself: for each password
 an extended attribute `trusted.fscrypt_slot0`, `trusted.fscrypt_slot1`,
-`trusted.fscrypt_slot2`, … is maintained. It's value contains a colon-separated
+`trusted.fscrypt_slot2`, … is maintained. Its value contains a colon-separated
 pair of Base64 encoded data fields. The first field contains a salt value, the
 second field the encrypted volume key. The latter is encrypted using AES256 in
-counter mode, using a key derived from the password via PBKDF2-HMAC-SHA512
+counter mode, using a key derived from the password via PBKDF2-HMAC-SHA512,
 together with the salt value. The construction is similar to what LUKS does for
 `dm-crypt` encrypted volumes. Note that extended attributes are not encrypted
-by `fscrypt` and hence are suitable for carry the key slots. Moreover, by using
-extended attributes the slots are directly attached to the directory and an
-independent sidecar key database is not required.
+by `fscrypt` and hence are suitable for carrying the key slots. Moreover, by
+using extended attributes, the slots are directly attached to the directory and
+an independent sidecar key database is not required.
 
 ## Storage Mechanism: `cifs` Home Directories
 
-In this storage mechanism the home directory is mounted from a CIFS server and
+In this storage mechanism, the home directory is mounted from a CIFS server and
 service at login, configured inside the user record. (Use `--storage=cifs` on
 the `homectl` command line.) The local password of the user is used to log into
 the CIFS service. The directory share needs to contain the user record in
@@ -85,7 +85,7 @@ media). (Use `--storage=luks` on the `homectl` command line.)  Specifically:
 
 * The image contains a GPT partition table. For now it should only contain a
   single partition, and that partition must have the type UUID
-  `773f91ef-66d4-49b5-bd83-d683bf40ad16`. It's partition label must be the
+  `773f91ef-66d4-49b5-bd83-d683bf40ad16`. Its partition label must be the
   user name.
 
 * This partition must contain a LUKS2 volume, whose label must be the user
@@ -106,24 +106,24 @@ media). (Use `--storage=luks` on the `homectl` command line.)  Specifically:
   contains a second copy of the user record in the `~/.identity` file, like in
   the other storage mechanisms.
 
-The image file should either reside in a directory `/home/` on the system,
-named after the user, suffixed with `.home`. When activated the container home
+The image file should reside in a directory `/home/` on the system,
+named after the user, suffixed with `.home`. When activated, the container home
 directory is mounted to the same path, though with the `.home` suffix dropped —
 unless a different mount point is defined in the user record. (e.g.: the
 loopback file `/home/waldo.home` is mounted to `/home/waldo` while activated.)
-When the image is stored on removable media (such as a USB stick) the image
-file can be directly `dd`'ed onto it, the format is unchanged. The GPT envelope
+When the image is stored on removable media (such as a USB stick), the image
+file can be directly `dd`'ed onto it; the format is unchanged. The GPT envelope
 should ensure the image is properly recognizable as a home directory both when
 used in a loopback file and on a removable USB stick. (Note that when mounting
-a home directory from an USB stick it too defaults to a directory in `/home/`,
+a home directory from an USB stick, it too defaults to a directory in `/home/`,
 named after the username, with no further suffix.)
 
 Rationale for the GPT partition table envelope: this way the image is nicely
 discoverable and recognizable already by partition managers as a home
 directory. Moreover, when copied onto a USB stick the GPT envelope makes sure
 the stick is properly recognizable as a portable home directory
-medium. (Moreover it allows to embed additional partitions later on, for
-example for allowing a multi-purpose USB stick that contains both a home
+medium. (Moreover, it allows embedding additional partitions later on, for
+example on a multi-purpose USB stick that contains both a home
 directory and a generic storage volume.)
 
 Rationale for including the encrypted user record in the LUKS2 header:
@@ -133,7 +133,7 @@ images can be used as attack vectors, exploiting the kernel. Thus it is
 necessary to validate the home directory image *before* mounting it and
 establishing a minimal level of trust. Since the user record data is
 cryptographically signed and user records not signed with a recognized private
-key are not accepted a minimal level of trust between the system and the home
+key are not accepted, a minimal level of trust between the system and the home
 directory image is established.
 
 Rationale for storing the home directory one level below to root directory of
@@ -145,10 +145,10 @@ do not show up in the user's home directory.
 Regardless of the storage mechanism used, an activated home directory
 necessarily involves a mount point to be established. In case of the
 directory-based storage mechanisms (`directory`, `subvolume` and `fscrypt`)
-this is a bind mount, in case of `cifs` this is a CIFS network mount, and in
+this is a bind mount. In case of `cifs` this is a CIFS network mount, and in
 case of the LUKS2 backend a regular block device mount of the file system
 contained in the LUKS2 image. By requiring a mount for all cases (even for
-those that already are a directory) a clear logic is defined to distinguish
+those that already are a directory), a clear logic is defined to distinguish
 active and inactive home directories, so that the directories become
 inaccessible under their regular path the instant they are
 deactivated. Moreover, the `nosuid`, `nodev` and `noexec` flags configured in
@@ -161,15 +161,15 @@ compared. Activation is only permitted if they match the same user and are
 signed by a recognized key. When the three instances differ in `lastChangeUSec`
 field, the newest record wins, and is propagated to the other two locations.
 
-During activation the file system checker (`fsck`) appropriate for the
+During activation, the file system checker (`fsck`) appropriate for the
 selected file system is automatically invoked, ensuring the file system is in a
 healthy state before it is mounted.
 
 If the UID assigned to a user does not match the owner of the home directory in
 the file system, the home directory is automatically and recursively `chown()`ed
 to the correct UID.
 
-Depending on the `luksDiscard` setting of the user record either the backing
+Depending on the `luksDiscard` setting of the user record, either the backing
 loopback file is `fallocate()`ed during activation, or the mounted file system
 is `FITRIM`ed after mounting, to ensure the setting is correctly enforced.
 
