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In Unix-like systems, multiple users can be combined to form groups. POSIX and conventional Unix file system permissions are organized into three classes, user, group, and others. The use of groups allows additional abilities to be delegated in an organized fashion, such as access to disks, printers, and other peripherals. This method, amongst others, also enables the Superuser to delegate some administrative tasks to normal users, similar to the Administrators group on Microsoft Windows NT and its derivatives. A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ...
POSIX is the collective name of a family of related standards specified by the IEEE to define the application program interface (API) for software designed to run on variants of the Unix OS. They are formally designated as IEEE 1003 and the international standard name is ISO/IEC 9945. ...
Wikibooks has more about this subject: Guide to UNIX Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ...
Most modern file systems have methods of administering permissions or access rights to specific users and groups of users. ...
A computer printer is a computer peripheral device that produces a hard copy (permanent human-readable text and/or graphics, usually on paper) from data stored in a computer connected to it. ...
A peripheral ***is ***a ***type ******of ***************computer ***hardware************ ***that ***is ***added ***to ***a ***host ******computer*** ******in ***order ************to ***expand ***its abilities***. ***More ***specifica************lly ***the term ***is ***used ***to describe ***those ***devices ***that ***are optional ***in ***nature***, as ***opposed ***t*********o ***hardware ***that ***is ***either ***demanded***, ***or ***always r*********equired...
On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ...
Windows NT is a family of operating systems produced by Microsoft, and was succeeded by Windows 2000 (still based on Windows NT). ...
A group identifier, often abbreviated to GID, is a numeric value used to represent a specific group. The range of values for a GID varies amongst different systems; at the very least, a GID can be between 0 and 32767, with one restriction: the login group for the Superuser must have GID 0. This numeric value is used to refer to groups in the /etc/passwd and /etc/group files or their equivalents. Shadow password files and Network Information Service also refer to numeric GIDs. The group identifier is a necessary component of Unix file systems and processes. On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ...
The process of shadowing passwords is used to increase the security level of passwords on Unix systems. ...
The Network Information Service or NIS is Sun Microsystems Yellow Pages (YP) client-server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network. ...
Wikibooks has more about this subject: Guide to UNIX Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ...
In computing, a file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ...
In computing, a process is a running instance of a program, including all variables and other state. ...
The limits on the range of possible group identifiers come from the memory space used to store them. Originally, a signed 16-bit integer was used. Realizing that sign was not necessary—negative numbers don't make valid group IDs—an unsigned integer was used instead, allowing group IDs between 0 and 65535. Modern operating systems usually use unsigned 32-bit integers, which allow for group IDs between 0 and 4294967295. The switch from 16 to 32 bits was originally not necessary—one machine or even one network did not serve more than 65536 users at the time—but was made to elimate the need to do so in the future, when it would be more difficult to implement.
Primary v.s. Supplementary Group IDs
In Unix systems, every user must be a member of at least one group, which is identified by the numeric GID of the user's entry in /etc/passwd. This group is referred to as the primary group ID. A user may be listed as members of additional groups in the relevant groups entry in the /etc/group; the IDs of these groups are referred to as supplementary group IDs. The Filesystem Hierarchy Standard (FHS) defines the main directories and their contents in Linux and other Unix-like computer operating systems. ...
Effective v.s. Real Group IDs Unix processes have both an effective and a real group ID. Normally these are identically, but in setgid process they are different. This is so the setgid process can perform privileged functions using the privileged group, yet easily revert to the non-privileged group when necessary. This is to prevent the calling user does not from manipulating the process to gain unauthorised access to the privileged group. Setuid is a UNIX term, and is short for Set User ID. Setuid, also sometimes referred to as suid, is an access right flag that can be assigned to files and directories on a UNIX based operating system. ...
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