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Full Discussion: What is a daemon process?
Top Forums Programming What is a daemon process? Post 16250 by Perderabo on Wednesday 27th of February 2002 09:49:09 AM
Old 02-27-2002
A daemon process has no controlling terminal. It cannot open /dev/tty. If you do a "ps -ef" and look at the tty field, all daemons will have a ? for the tty.

Most daemons tend to last a long time, be owned by root, and do something useful. But you really can't count on any of these thing being true.

The lack of a controlling terminal is the real defining characteristic.
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OPENPTY(3)						   BSD Library Functions Manual 						OPENPTY(3)

NAME
openpty, login_tty, forkpty -- tty utility functions SYNOPSIS
#include <util.h> int openpty(int *amaster, int *aslave, char *name, struct termios *termp, struct winsize *winp); int login_tty(int fd); pid_t forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp); DESCRIPTION
The openpty(), login_tty(), and forkpty() functions perform manipulations on ttys and pseudo-ttys. The openpty() function allocates a pseudo-tty and returns file descriptors for the master and slave in amaster and aslave. If name is non- null, the filename of the slave is returned in name. If termp is non-null, the terminal parameters of the slave will be set to the values in termp. If winp is non-null, the window size of the slave will be set to the values in winp. The login_tty() function prepares for a login on the tty fd (which may be a real tty device, or the slave of a pseudo-tty as returned by openpty()) by creating a new session, making fd the controlling terminal for the current process, setting fd to be the standard input, out- put, and error streams of the current process, and closing fd. The forkpty() function combines openpty(), fork(), and login_tty() to creates a new process operating in a pseudo-tty. The file descriptor of the master side of the pseudo-tty is returned in amaster, and the filename of the slave in name if it is non-null. The termp and winp parameters, if non-null, will determine the terminal attributes and window size of the slave side of the pseudo-tty. RETURN VALUES
If a call to openpty(), login_tty(), or forkpty() is not successful, -1 is returned and errno is set to indicate the error. Otherwise, openpty(), login_tty(), and the child process of forkpty() return 0, and the parent process of forkpty() returns the process ID of the child process. ERRORS
openpty() will fail if: [EAGAIN] There are no available pseudo-ttys. login_tty() will fail if ioctl() fails to set fd to the controlling terminal of the current process. forkpty() will fail if either openpty() or fork() fails. FILES
/dev/ptmx cloning pseudo-tty device /dev/ttys[0-9][0-9][0-9] slave pseudo-tty devices SEE ALSO
fork(2) BSD
April 5, 2008 BSD
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