Concept
Init
Related concepts (18)
Runlevel
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). A runlevel defines the state of the machine after boot.
Systemd
Systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions. Its primary component is a "system and service manager" – an init system used to bootstrap user space and manage user processes. It also provides replacements for various daemons and utilities, including device management, login management, network connection management, and event logging.
Linux
Linux (ˈlɪnʊks ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which includes the kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name "GNU/Linux" to emphasize the use and importance of GNU software in many distributions, causing some controversy.
Parent process
In computing, a parent process is a process that has created one or more child processes. In Unix-like operating systems, every process except process 0 (the swapper) is created when another process executes the fork() system call. The process that invoked fork is the parent process and the newly created process is the child process. Every process (except process 0) has one parent process, but can have many child processes. The operating system kernel identifies each process by its process identifier.
Zombie process
On Unix and Unix-like computer operating systems, a zombie process or defunct process is a process that has completed execution (via the exit system call) but still has an entry in the process table: it is a process in the "Terminated state". This occurs for the child processes, where the entry is still needed to allow the parent process to read its child's exit status: once the exit status is read via the wait system call, the zombie's entry is removed from the process table and it is said to be "reaped".
Udev
udev (userspace ) is a device manager for the Linux kernel. As the successor of devfsd and hotplug, udev primarily manages device nodes in the directory. At the same time, udev also handles all user space events raised when hardware devices are added into the system or removed from it, including firmware loading as required by certain devices. It is an operating system's kernel that is responsible for providing an abstract interface of the hardware to the rest of the software.
Cron
The cron command-line utility is a job scheduler on Unix-like operating systems. Users who set up and maintain software environments use cron to schedule jobs (commands or shell scripts), also known as cron jobs, to run periodically at fixed times, dates, or intervals. It typically automates system maintenance or administration—though its general-purpose nature makes it useful for things like downloading files from the Internet and downloading email at regular intervals. Cron is most suitable for scheduling repetitive tasks.
Daemon (computing)
In multitasking computer operating systems, a daemon (ˈdiːmən or ˈdeɪmən) is a computer program that runs as a background process, rather than being under the direct control of an interactive user. Traditionally, the process names of a daemon end with the letter d, for clarification that the process is in fact a daemon, and for differentiation between a daemon and a normal computer program. For example, is a daemon that implements system logging facility, and is a daemon that serves incoming SSH connections.
Launchd
launchd is an init and operating system service management daemon created by Apple Inc. as part of macOS to replace its BSD-style init and SystemStarter. There have been efforts to port launchd to FreeBSD and derived systems. There are two main programs in the launchd system: launchd and launchctl. launchd manages the daemons at both a system and user level. Similar to xinetd, launchd can start daemons on demand. Similar to watchdogd, launchd can monitor daemons to make sure that they keep running.
Exit (system call)
On many computer operating systems, a computer process terminates its execution by making an exit system call. More generally, an exit in a multithreading environment means that a thread of execution has stopped running. For resource management, the operating system reclaims resources (memory, , etc.) that were used by the process. The process is said to be a dead process after it terminates. Under Unix and Unix-like operating systems, a process is started when its parent process executes a fork system call.