Unix

Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, the development of which started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley (BSD), Microsoft (Xenix), Sun Microsystems (SunOS/Solaris), HP/HPE (HP-UX), and IBM (AIX).

thumb|upright=1.8|Evolution of Unix and Unix-like systems, starting in 1969|class=skin-invert-image

problem affecting digital systems that store system time as a signed 32-bit integer

system for identifying instants in time; the number of seconds that have elapsed since the UTC midnight before 1 January 1970, ignoring leap seconds

industry consortium working for open, unified standards for Unix systems

the symbol "#!", used in computing at the beginning of a shell script to specify an interpreter

philosophy on developing software

A runlevel is a mode of operation in the computer operating systems that implements Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six. S is sometimes used as a synonym for one of the levels. Only one runlevel is executed on startup; run levels are not executed one after another (i.e. only runlevel 2, 3, or 4 is executed, not more of them sequentially or in any other order).

preconnected input and output streams for computer programs

socket for exchanging data between processes executing on the same OS; similar to an Internet socket, but all communication occurs within the same OS

numeric value used in Unix-like operating systems to uniquely identify a user account

thumb|USENIX booth at Linuxcon 2016

set of Unix processes chained by their standard streams

form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations

Unix/POSIX system account group number; numeric value used to represent a specific group

operating system mechanism

In computer networking, xinetd (Extended Internet Service Daemon) is an open-source super-server daemon which runs on many Unix-like systems, and manages Internet-based connectivity.

communications protocol

In computing, ioctl (an abbreviation of input/output control) is a system call for device-specific input/output operations and other operations which cannot be expressed by read/write/seek regular file semantics. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are often device-specific. For instance, a CD-ROM device driver which can instruct a physical device to eject a disc would provide an ioctl request code to do so. Device-independent request codes are sometimes used to give userspace access to kernel functions whic

small file shown to every user of the system after login

control of jobs by a Unix shell

user account on a remote server

sysctl is a software mechanism in some Unix-like operating systems that reads and modifies the attributes of the system kernel such as its version number, maximum limits, and security settings. It is available both as a system call for compiled programs, and an administrator command for interactive use and scripting. Linux additionally exposes sysctl as a virtual file system.

general information field in UNIX password files

conventional name for a type of user account in Unix systems

ptrace is a system call found in Unix and several Unix-like operating systems. By using ptrace (an abbreviation of "process trace") one process can control another, enabling the controller to inspect and manipulate the internal state of its target. ptrace is used by debuggers and other code-analysis tools, mostly as aids to software development.

type of user account in Unix