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