03-25-2009
The third option to open() - which is shown in man pages as "..." is only used when a new file is being created. In your case you are opening an existing file as read only.
"..." is a way of saying that the number and types of the remaining arguments may vary. There may be none or there may be one or more.
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PTS(4) Linux Programmer's Manual PTS(4)
NAME
ptmx, pts - pseudoterminal master and slave
DESCRIPTION
The file /dev/ptmx is a character file with major number 5 and minor number 2, usually of mode 0666 and owner.group of root.root. It is
used to create a pseudoterminal master and slave pair.
When a process opens /dev/ptmx, it gets a file descriptor for a pseudoterminal master (PTM), and a pseudoterminal slave (PTS) device is
created in the /dev/pts directory. Each file descriptor obtained by opening /dev/ptmx is an independent PTM with its own associated PTS,
whose path can be found by passing the file descriptor to ptsname(3).
Before opening the pseudoterminal slave, you must pass the master's file descriptor to grantpt(3) and unlockpt(3).
Once both the pseudoterminal master and slave are open, the slave provides processes with an interface that is identical to that of a real
terminal.
Data written to the slave is presented on the master file descriptor as input. Data written to the master is presented to the slave as
input.
In practice, pseudoterminals are used for implementing terminal emulators such as xterm(1), in which data read from the pseudoterminal mas-
ter is interpreted by the application in the same way a real terminal would interpret the data, and for implementing remote-login programs
such as sshd(8), in which data read from the pseudoterminal master is sent across the network to a client program that is connected to a
terminal or terminal emulator.
Pseudoterminals can also be used to send input to programs that normally refuse to read input from pipes (such as su(1), and passwd(1)).
FILES
/dev/ptmx, /dev/pts/*
NOTES
The Linux support for the above (known as UNIX 98 pseudoterminal naming) is done using the devpts filesystem, that should be mounted on
/dev/pts.
Before this UNIX 98 scheme, master pseudoterminals were called /dev/ptyp0, ... and slave pseudoterminals /dev/ttyp0, ... and one needed
lots of preallocated device nodes.
SEE ALSO
getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2016-03-15 PTS(4)