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diff --git a/docs/GROUP_RECORD.md b/docs/GROUP_RECORD.md new file mode 100644 index 0000000..0180049 --- /dev/null +++ b/docs/GROUP_RECORD.md @@ -0,0 +1,162 @@ +--- +title: JSON Group Records +category: Users, Groups and Home Directories +layout: default +--- + +# JSON Group Records + +Long story short: JSON Group Records are to `struct group` what [JSON User +Records](https://systemd.io/USER_RECORD.md) are to `struct passwd`. + +Conceptually, much of what applies to JSON user records also applies to JSON +group records. They also consist of seven sections, with similar properties and +they carry some identical (or at least very similar) fields. + +## Fields in the `regular` section + +`groupName` → A string with the UNIX group name. Matches the `gr_name` field of +UNIX/glibc NSS `struct group`, or the shadow structure `struct sgrp`'s +`sg_namp` field. + +`realm` → The "realm" the group belongs to, conceptually identical to the same +field of user records. A string in DNS domain name syntax. + +`description` → A descriptive string for the group. This is similar to the +`realName` field of user records, and accepts arbitrary strings, as long as +they follow the same GECOS syntax requirements as `realName`. + +`disposition` → The disposition of the group, conceptually identical to the +same field of user records. A string. + +`service` → A string, an identifier for the service managing this group record +(this field is typically in reverse domain name syntax.) + +`lastChangeUSec` → An unsigned 64bit integer, a timestamp (in µs since the UNIX +epoch 1970) of the last time the group record has been modified. (Covers only +the `regular`, `perMachine` and `privileged` sections). + +`gid` → An unsigned integer in the range 0…4294967295: the numeric UNIX group +ID (GID) to use for the group. This corresponds to the `gr_gid` field of +`struct group`. + +`members` → An array of strings, listing user names that are members of this +group. Note that JSON user records also contain a `memberOf` field, or in other +words a group membership can either be denoted in the JSON user record or in +the JSON group record, or in both. The list of memberships should be determined +as the combination of both lists (plus optionally others). If a user is listed +as member of a group and doesn't exist it should be ignored. This field +corresponds to the `gr_mem` field of `struct group` and the `sg_mem` field of +`struct sgrp`. + +`administrators` → Similarly, an array of strings, listing user names that +shall be considered "administrators" of this group. This field corresponds to +the `sg_adm` field of `struct sgrp`. + +`privileged`/`perMachine`/`binding`/`status`/`signature`/`secret` → The +objects/arrays for the other six group record sections. These are organized the +same way as for the JSON user records, and have the same semantics. + +## Fields in the `privileged` section + +The following fields are defined: + +`hashedPassword` → An array of strings with UNIX hashed passwords; see the +matching field for user records for details. This field corresponds to the +`sg_passwd` field of `struct sgrp` (and `gr_passwd` of `struct group` in a +way). + +## Fields in the `perMachine` section + +`matchMachineId`/`matchHostname` → Strings, match expressions similar as for +user records, see the user record documentation for details. + +The following fields are defined for the `perMachine` section and are defined +equivalent to the fields of the same name in the `regular` section, and +override those: + +`gid`, `members`, `administrators` + +## Fields in the `binding` section + +The following fields are defined for the `binding` section, and are equivalent +to the fields of the same name in the `regular` and `perMachine` sections: + +`gid` + +## Fields in the `status` section + +The following fields are defined in the `status` section, and are mostly +equivalent to the fields of the same name in the `regular` section, though with +slightly different conceptual semantics, see the same fields in the user record +documentation: + +`service` + +## Fields in the `signature` section + +The fields in this section are defined identically to those in the matching +section in the user record. + +## Fields in the `secret` section + +Currently no fields are defined in this section for group records. + +## Mapping to `struct group` and `struct sgrp` + +When mapping classic UNIX group records (i.e. `struct group` and `struct sgrp`) +to JSON group records the following mappings should be applied: + +| Structure | Field | Section | Field | Condition | +|----------------|-------------|--------------|------------------|----------------------------| +| `struct group` | `gr_name` | `regular` | `groupName` | | +| `struct group` | `gr_passwd` | `privileged` | `password` | (See notes below) | +| `struct group` | `gr_gid` | `regular` | `gid` | | +| `struct group` | `gr_mem` | `regular` | `members` | | +| `struct sgrp` | `sg_namp` | `regular` | `groupName` | | +| `struct sgrp` | `sg_passwd` | `privileged` | `password` | (See notes below) | +| `struct sgrp` | `sg_adm` | `regular` | `administrators` | | +| `struct sgrp` | `sg_mem` | `regular` | `members` | | + +At this time almost all Linux machines employ shadow passwords, thus the +`gr_passwd` field in `struct group` is set to `"x"`, and the actual password +is stored in the shadow entry `struct sgrp`'s field `sg_passwd`. + +## Extending These Records + +The same logic and recommendations apply as for JSON user records. + +## Examples + +A reasonable group record for a system group might look like this: + +```json +{ + "groupName" : "systemd-resolve", + "gid" : 193, + "status" : { + "6b18704270e94aa896b003b4340978f1" : { + "service" : "io.systemd.NameServiceSwitch" + } + } +} +``` + +And here's a more complete one for a regular group: + +```json +{ + "groupName" : "grobie", + "binding" : { + "6b18704270e94aa896b003b4340978f1" : { + "gid" : 60232 + } + }, + "disposition" : "regular", + "status" : { + "6b18704270e94aa896b003b4340978f1" : { + "service" : "io.systemd.Home" + } + } +} +``` |