Below is a table of required mnemonic user and group names. This specification makes no attempt to numerically assign uid or gid numbers. The exception is the uid and gid for "root" which are equal to 0.
Table 17-1. Required User & Group Names
| User | Group | Comments |
| root | root | Administrative user with no restrictions |
| bin | bin | Legacy UID/GID[a] |
| daemon | daemon | Legacy UID/GID[b] |
| Notes: a. The 'bin' UID/GID is included for compatibility with legacy applications. New applications should no longer use the 'bin' UID/GID. b. The 'daemon' UID/GID was used as an unprivileged UID/GID for daemons to execute under in order to limit their access to the system. Generally daemons should now run under individual UID/GIDs in order to further partition daemons from one another. | ||
Below is a table of optional mnemonic user and group names. This specification makes no attempt to numerically assign uid or gid numbers. If the username exists on a system, then they should be in the suggested corresponding group. These user and group names are for use by distributions, not by applications.
Table 17-2. Optional User & Group Names
| User | Group | Comments |
| adm | adm | Administrative special privileges |
| lp | lp | Printer special privileges |
| sync | sync | Login to sync the system |
| shutdown | shutdown | Login to shutdown the system |
| halt | halt | Login to halt the system |
| Mail special privileges | ||
| news | news | News special privileges |
| uucp | uucp | UUCP special privileges |
| operator | root | Operator special privileges |
| man | man | Man special privileges |
| nobody | nobody | Used by NFS |
The differences in numeric values of the uids and gids between systems on a network can be reconciled via NIS, rdist(1), rsync(1), or ugidd(8). Only a minimum working set of "user names" and their corresponding "user groups" are required. Applications cannot assume non system user or group names will be defined.
Applications cannot assume any policy for the default umask or the default directory permissions a user may have. Applications should enforce user only file permissions on private files such as mailboxes. The location of the users home directory is also not defined by policy other than the recommendations of the FHS and must be obtained by the *pwnam(3) calls.