docs/GROUP_RECORD.md

   1 ---
   2 title: JSON Group Records
   3 category: Users, Groups and Home Directories
   4 layout: default
   5 ---
   6
   7 # JSON Group Records
   8
   9 Long story short: JSON Group Records are to `struct group` what [JSON User
  10 Records](https://systemd.io/USER_RECORD.md) are to `struct passwd`.
  11
  12 Conceptually, much of what applies to JSON user records also applies to JSON
  13 group records. They also consist of seven sections, with similar properties and
  14 they carry some identical (or at least very similar) fields.
  15
  16 ## Fields in the `regular` section
  17
  18 `groupName` → A string with the UNIX group name. Matches the `gr_name` field of
  19 UNIX/glibc NSS `struct group`, or the shadow structure `struct sgrp`'s
  20 `sg_namp` field.
  21
  22 `realm` → The "realm" the group belongs to, conceptually identical to the same
  23 field of user records. A string in DNS domain name syntax.
  24
  25 `description` → A descriptive string for the group. This is similar to the
  26 `realName` field of user records, and accepts arbitrary strings, as long as
  27 they follow the same GECOS syntax requirements as `realName`.
  28
  29 `disposition` → The disposition of the group, conceptually identical to the
  30 same field of user records. A string.
  31
  32 `service` → A string, an identifier for the service managing this group record
  33 (this field is typically in reverse domain name syntax.)
  34
  35 `lastChangeUSec` → An unsigned 64bit integer, a timestamp (in µs since the UNIX
  36 epoch 1970) of the last time the group record has been modified. (Covers only
  37 the `regular`, `perMachine` and `privileged` sections).
  38
  39 `gid` → An unsigned integer in the range 0…4294967295: the numeric UNIX group
  40 ID (GID) to use for the group. This corresponds to the `gr_gid` field of
  41 `struct group`.
  42
  43 `members` → An array of strings, listing user names that are members of this
  44 group. Note that JSON user records also contain a `memberOf` field, or in other
  45 words a group membership can either be denoted in the JSON user record or in
  46 the JSON group record, or in both. The list of memberships should be determined
  47 as the combination of both lists (plus optionally others). If a user is listed
  48 as member of a group and doesn't exist it should be ignored. This field
  49 corresponds to the `gr_mem` field of `struct group` and the `sg_mem` field of
  50 `struct sgrp`.
  51
  52 `administrators` → Similarly, an array of strings, listing user names that
  53 shall be considered "administrators" of this group. This field corresponds to
  54 the `sg_adm` field of `struct sgrp`.
  55
  56 `privileged`/`perMachine`/`binding`/`status`/`signature`/`secret` → The
  57 objects/arrays for the other six group record sections. These are organized the
  58 same way as for the JSON user records, and have the same semantics.
  59
  60 ## Fields in the `privileged` section
  61
  62 The following fields are defined:
  63
  64 `hashedPassword` → An array of strings with UNIX hashed passwords; see the
  65 matching field for user records for details. This field corresponds to the
  66 `sg_passwd` field of `struct sgrp` (and `gr_passwd` of `struct group` in a
  67 way).
  68
  69 ## Fields in the `perMachine` section
  70
  71 `matchMachineId`/`matchHostname` → Strings, match expressions similar as for
  72 user records, see the user record documentation for details.
  73
  74 The following fields are defined for the `perMachine` section and are defined
  75 equivalent to the fields of the same name in the `regular` section, and
  76 override those:
  77
  78 `gid`, `members`, `administrators`
  79
  80 ## Fields in the `binding` section
  81
  82 The following fields are defined for the `binding` section, and are equivalent
  83 to the fields of the same name in the `regular` and `perMachine` sections:
  84
  85 `gid`
  86
  87 ## Fields in the `status` section
  88
  89 The following fields are defined in the `status` section, and are mostly
  90 equivalent to the fields of the same name in the `regular` section, though with
  91 slightly different conceptual semantics, see the same fields in the user record
  92 documentation:
  93
  94 `service`
  95
  96 ## Fields in the `signature` section
  97
  98 The fields in this section are defined identically to those in the matching
  99 section in the user record.
 100
 101 ## Fields in the `secret` section
 102
 103 Currently no fields are defined in this section for group records.
 104
 105 ## Mapping to `struct group` and `struct sgrp`
 106
 107 When mapping classic UNIX group records (i.e. `struct group` and `struct sgrp`)
 108 to JSON group records the following mappings should be applied:
 109
 110 | Structure      | Field       | Section      | Field            | Condition                  |
 111 |----------------|-------------|--------------|------------------|----------------------------|
 112 | `struct group` | `gr_name`   | `regular`    | `groupName`      |                            |
 113 | `struct group` | `gr_passwd` | `privileged` | `password`       | (See notes below)          |
 114 | `struct group` | `gr_gid`    | `regular`    | `gid`            |                            |
 115 | `struct group` | `gr_mem`    | `regular`    | `members`        |                            |
 116 | `struct sgrp`  | `sg_namp`   | `regular`    | `groupName`      |                            |
 117 | `struct sgrp`  | `sg_passwd` | `privileged` | `password`       | (See notes below)          |
 118 | `struct sgrp`  | `sg_adm`    | `regular`    | `administrators` |                            |
 119 | `struct sgrp`  | `sg_mem`    | `regular`    | `members`        |                            |
 120
 121 At this time almost all Linux machines employ shadow passwords, thus the
 122 `gr_passwd` field in `struct group` is set to `"x"`, and the actual password
 123 is stored in the shadow entry `struct sgrp`'s field `sg_passwd`.
 124
 125 ## Extending These Records
 126
 127 The same logic and recommendations apply as for JSON user records.
 128
 129 ## Examples
 130
 131 A reasonable group record for a system group might look like this:
 132
 133 ```json
 134 {
 135         "groupName" : "systemd-resolve",
 136         "gid" : 193,
 137         "status" : {
 138                 "6b18704270e94aa896b003b4340978f1" : {
 139                         "service" : "io.systemd.NameServiceSwitch"
 140                 }
 141         }
 142 }
 143 ```
 144
 145 And here's a more complete one for a regular group:
 146
 147 ```json
 148 {
 149         "groupName" : "grobie",
 150         "binding" : {
 151                 "6b18704270e94aa896b003b4340978f1" : {
 152                         "gid" : 60232
 153                 }
 154         },
 155         "disposition" : "regular",
 156         "status" : {
 157                 "6b18704270e94aa896b003b4340978f1" : {
 158                         "service" : "io.systemd.Home"
 159                 }
 160         }
 161 }
 162 ```