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close(2) [minix man page]

CLOSE(2)							System Calls Manual							  CLOSE(2)

NAME
close - delete a descriptor SYNOPSIS
#include <unistd.h> int close(int d) DESCRIPTION
The close call deletes a descriptor from the per-process object reference table. If this is the last reference to the underlying object, then it will be deactivated. For example, on the last close of a file the current seek pointer associated with the file is lost; on the last close of a TCP/IP descriptor associated naming information and queued data are discarded; on the last close of a file holding an advi- sory lock the lock is released (see further fcntl(2)). A close of all of a process's descriptors is automatic on exit, but since there is a limit on the number of active descriptors per process, close is necessary for programs that deal with many descriptors. When a process forks (see fork(2)), all descriptors for the new child process reference the same objects as they did in the parent before the fork. If a new process is then to be run using execve(2), the process would normally inherit these descriptors. Most of the descrip- tors can be rearranged with dup2(2) or deleted with close before the execve is attempted, but if some of these descriptors will still be needed if the execve fails, it is necessary to arrange for them to be closed if the execve succeeds. For this reason, the call ``fcntl(d, F_SETFD, flags)'' is provided, that can be used to mark a descriptor "close on exec" by setting the FD_CLOEXEC flag: fcntl(d, F_SETFD, fcntl(d, F_GETFD) | FD_CLOEXEC); RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error. ERRORS
Close will fail if: [EBADF] D is not an active descriptor. SEE ALSO
open(2), pipe(2), execve(2), fcntl(2). 4th Berkeley Distribution May 22, 1986 CLOSE(2)

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DUP(2)								System Calls Manual							    DUP(2)

NAME
dup, dup2 - duplicate a descriptor SYNOPSIS
#include <unistd.h> int dup(int oldd) int dup2(int oldd, int newd) DESCRIPTION
Dup duplicates an existing descriptor. The argument oldd is a small non-negative integer index in the per-process descriptor table. The value must be less than OPEN_MAX, the size of the table. The new descriptor returned by the call, let's name it newd, is the lowest num- bered descriptor that is not currently in use by the process. The object referenced by the descriptor does not distinguish between references using oldd and newd in any way. Thus if newd and oldd are duplicate references to an open file, read(2), write(2) and lseek(2) calls all move a single pointer into the file, and append mode, non- blocking I/O and asynchronous I/O options are shared between the references. If a separate pointer into the file is desired, a different object reference to the file must be obtained by issuing an additional open(2) call. The close-on-exec flag on the new file descriptor is unset. In the second form of the call, the value of newd desired is specified. If this descriptor is already in use, the descriptor is first deallocated as if a close(2) call had been done first. Newd is not closed if it equals oldd. RETURN VALUE
The value -1 is returned if an error occurs in either call. The external variable errno indicates the cause of the error. ERRORS
Dup and dup2 fail if: [EBADF] Oldd or newd is not a valid active descriptor [EMFILE] Too many descriptors are active. NOTES
Dup and dup2 are now implemented using the F_DUPFD function of fcntl(2), although the old system call interfaces still exist to support old programs. SEE ALSO
open(2), close(2), fcntl(2), pipe(2). 4th Berkeley Distribution May 13, 1986 DUP(2)
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