UidNumber is a Number as used in POSIX systems for Identification of the user.

UidNumber the UID or UserId) which is a number assigned by Linux and UNIX to each user on the system. This number is used to identify the user to the system and to determine which system resources the user can access. UidNumber is the AttributeType used in LDAP for the storing the number

LDAP Attribute Definition#

The UidNumber AttributeTypes is defined as:

Even more complex is the situation around nobody. The user nobody and group nogroup came from the NFS software and was defined as being having the highest UidNumber, since the function was oposite to the root:

  • 16-bit systems: 65,536 unique UidNumbers
  • 32-bit systems: 4,294,967,296 unique UidNumbers

This resulted in some confusion. To this confusion was added the use of using -2 for the nobody ID, as was done by the software itself if nobody and nogroup where not defined. GNU/Linux distribution creators defined the account as 65534, however Red Hat supplied under that UidNumber nfsnobody with another nobody having UidNumber 99. And there is nogroup usage, but also groups that are called nobody. All in all a rough overview of what is used where can be created like this:

-2nobody on AIX and MacOS
0-99Unix local users and groups, statically assigned
99Red Hat based system nobody user and group UidNumber
100-499Unix local users and groups, dynamic
529Used as UidNumber for nobody on some systems (and not used by Microsoft)
32767Historic reservation for nobody (have not find any use)
60001Nobody on IRIX and SunOS
65530-65535Unix nobody user and (no)group (Debian and nfsnobody RHEL)
4294967292Group-owner on Isilon BSD
4294967293Null user on Isilon BSD
4294967294Everyone on Isilon BSD
4294967295Nobody (32-bit)

More Information#

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