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Full Discussion: file descriptors
Top Forums UNIX for Dummies Questions & Answers file descriptors Post 46836 by fpmurphy on Tuesday 27th of January 2004 06:46:14 PM
Old 01-27-2004
Note that processes do not have a limit of 20 file descriptors
as suggested in your mail - rather the limit is OPEN_MAX.

Here is the formal POSIX definition of a file descriptor:

A per-process unique, non-negative integer used to identify an open file for the purpose of file access. The value of a file descriptor is from zero to OPEN_MAX. A process can have no more than OPEN_MAX file descriptors open simultaneously.

Note also the difference between file DESCRIPTOR and file DESCRIPTION. From SUSv3 ....

(Open) File Description

A record of how a process or group of processes is accessing a file. Each file descriptor refers to exactly one open file description, but an open file description can be referred to by more than one file descriptor. The file offset, file status, and file access modes are attributes of an open file description.

- Finnbarr
 

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LEARN ABOUT HPUX

posix_openpt

posix_openpt(3C)														  posix_openpt(3C)

NAME

       posix_openpt() - open a pseudo-terminal master device

SYNOPSIS

   Parameters
       oflag	 indicates  the  file  status flags and file access modes of the open file description. Values for oflag are constructed by a bit-
		 wise-inclusive OR of flags from the following list, defined in

		 Open for reading and writing.

		 If set    will not cause the terminal device to become the controlling terminal for the process.

DESCRIPTION

       The function establishes a connection between a master device for a pseudo-terminal and a file descriptor. This file descriptor can be used
       to  refer  that	device.   The  file status flags and file access modes of the opened file descriptor will be set according to the value of
       oflag.

RETURN VALUE

       Upon successful completion opens a master pseudo-terminal device and returns a non-negative integer representing the lowest numbered unused
       file descriptor. Otherwise, returns -1 and is set to indicate the error.

ERRORS

       On failure sets one of the following values for

       OPEN_MAX       file descriptors are currently open in the calling process.

       The maximum allowable number of files are currently open on the system.

       The value of   oflag is not valid.

       Out of pseudo-terminal resources.

       Out of STREAMS resources.

AUTHOR

       was developed by HP.

SEE ALSO

       open(2), grantpt(3C), ptsname(3C), unlockpt(3C), ptm(7), pts(7).

																  posix_openpt(3C)
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