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| Original author(s) | Dennis Ritchie, Ken Thompson |
|---|---|
| Developer(s) | AT&T Bell Laboratories |
| Initial release | November 3, 1971 |
| Operating system | Unix and Unix-like |
| Platform | Cross-platform |
| Type | Command |
In Unix and Unix-like operating systems, write is a utility used to send messages to another user by writing a message directly to another user's TTY. [1]
The write command was included in the First Edition of the Research Unix operating system. [2] A similar command appeared in Compatible Time-Sharing System. [3]
The syntax for the write command is:
$ write user [tty]messageThe write session is terminated by sending EOF, which can be done by pressing Ctrl+D. The tty argument is only necessary when a user is logged into more than one terminal. [4]
A conversation initiated between two users on the same machine:
$ write root pts/7 testWill show up to the user on that console as:
Message from root@wiki on pts/8 at 11:19 ...test
A man page is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs, formal standards and conventions, and even abstract concepts. A user may invoke a man page by issuing the man command.
In Unix-like and some other operating systems, the pwd command writes the full pathname of the current working directory to the standard output.
In some operating systems, the null device is a device file that discards all data written to it but reports that the write operation succeeded. This device is called /dev/null on Unix and Unix-like systems, NUL: or NUL on CP/M and DOS, nul on OS/2 and newer Windows systems, NIL: on Amiga operating systems, and NL: on OpenVMS. In Windows Powershell, the equivalent is $null. It provides no data to any process that reads from it, yielding EOF immediately. In IBM operating systems DOS/360 and successors and also in OS/360 and successors such files would be assigned in JCL to DD DUMMY.
RSTS is a multi-user time-sharing operating system developed by Digital Equipment Corporation for the PDP-11 series of 16-bit minicomputers. The first version of RSTS was implemented in 1970 by DEC software engineers that developed the TSS-8 time-sharing operating system for the PDP-8. The last version of RSTS was released in September 1992. RSTS-11 and RSTS/E are usually referred to just as "RSTS" and this article will generally use the shorter form. RSTS-11 supports the BASIC programming language, an extended version called BASIC-PLUS, developed under contract by Evans Griffiths & Hart of Boston. Starting with RSTS/E version 5B, DEC added support for additional programming languages by emulating the execution environment of the RT-11 and RSX-11 operating systems.
In multitasking computer operating systems, a daemon 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, syslogd is a daemon that implements system logging facility, and sshd is a daemon that serves incoming SSH connections.
In computing, "Not a typewriter" or ENOTTY is an error code defined in the errno.h found on many Unix systems. This code is now used to indicate that an invalid ioctl number was specified in an ioctl system call.
passwd is a command on Unix, Plan 9, Inferno, and most Unix-like operating systems used to change a user's password. The password entered by the user is run through a key derivation function to create a hashed version of the new password, which is saved. Only the hashed version is stored; the entered password is not saved for security reasons.
A chroot on Unix and Unix-like operating systems is an operation that changes the apparent root directory for the current running process and its children. A program that is run in such a modified environment cannot name files outside the designated directory tree. The term "chroot" may refer to the chroot(2) system call or the chroot(8) wrapper program. The modified environment is called a chroot jail.
In most Unix and Unix-like operating systems, the ps program displays the currently-running processes. A related Unix utility named top provides a real-time view of the running processes.
In some operating systems, including Unix and Linux, a pseudoterminal, pseudotty, or PTY is a pair of pseudo-device endpoints (files) which establish asynchronous, bidirectional communication (IPC) channel between two or more processes. The master provides means by which a terminal emulator process controls the slave. The slave, emulates a hardware text terminal device. PTY are similar to bidirectional pipes.
In computing, echo is a command that outputs the strings that are passed to it as arguments. It is a command available in various operating system shells and typically used in shell scripts and batch files to output status text to the screen or a computer file, or as a source part of a pipeline.
Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems.
The standard Unix command who displays a list of users who are currently logged into the computer.
In Unix-based computer operating systems, init is the first process started during booting of the operating system. Init is a daemon process that continues running until the system is shut down. It is the direct or indirect ancestor of all other processes and automatically adopts all orphaned processes. Init is started by the kernel during the booting process; a kernel panic will occur if the kernel is unable to start it, or it should die for any reason. Init is typically assigned process identifier 1.
The proc filesystem (procfs) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized method for dynamically accessing process data held in the kernel than traditional tracing methods or direct access to kernel memory. Typically, it is mapped to a mount point named /proc at boot time. The proc file system acts as an interface to internal data structures about running processes in the kernel. In Linux, it can also be used to obtain information about the kernel and to change certain kernel parameters at runtime (sysctl).
wall is a Unix command-line utility that displays the contents of a computer file or standard input to all logged-in users. It is typically used by root to send out shutting down message to all users just before poweroff.
The command w on many Unix-like operating systems provides a quick summary of every user logged into a computer, what each user is currently doing, and what load all the activity is imposing on the computer itself. The command is a one-command combination of several other Unix programs: who, uptime, and ps -a.
In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow an application program to interact with a device by using its device driver via standard input/output system calls. Using standard system calls simplifies many programming tasks, and leads to consistent user-space I/O mechanisms regardless of device features and functions.
biff is a mail notification system for Unix.
A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and providing information to them as to what actions they are to perform. In some cases the invocation is conditional based on conditions established by the user or previous executables. Such access was first provided by computer terminals starting in the mid-1960s. This provided an interactive environment not available with punched cards or other input methods.
The basic concept of sending instantaneously messages to logged in users came with ... CTSS ...
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