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.
This User Gave Thanks to Perderabo For This Post:
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LEARN ABOUT MOJAVE
openpty
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