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close(2) [netbsd man page]

CLOSE(2)						      BSD System Calls Manual							  CLOSE(2)

close -- delete a descriptor LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> int close(int d); DESCRIPTION
The close() system call deletes a descriptor from the per-process object reference table. If this is the last reference to the underlying object, the object 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 socket(2) associated naming information and queued data are discarded; on the last close of a file holding an advisory lock the lock is released (see flock(2)). When a process exits, all associated descriptors are freed, but since there is a limit on active descriptors per processes, the close() sys- tem call is useful when a large quantity of file descriptors are being handled. When a process calls 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 descriptors 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 only if the execve() succeeds. For this reason, the system call fcntl(d, F_SETFD, 1); is provided, which arranges that a descriptor ``d'' will be closed after a successful execve(); the system call fcntl(d, F_SETFD, 0); restores the default, which is to not close descriptor ``d''. RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
close() will fail if: [EBADF] d is not an active descriptor. [EINTR] An interrupt was received. SEE ALSO
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2) STANDARDS
The close() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). BSD
April 19, 1994 BSD

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DUP(2)							      BSD System Calls Manual							    DUP(2)

dup, dup2 -- duplicate an existing file descriptor LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> int dup(int oldd); int dup2(int oldd, int newd); DESCRIPTION
The dup() system call duplicates an existing object descriptor and returns its value to the calling process (newd = dup(oldd)). The argument oldd is a small non-negative integer index in the per-process descriptor table. The new descriptor returned by the call is the lowest num- bered descriptor currently not in use by the process. The object referenced by the descriptor does not distinguish between oldd and newd in any way. Thus if newd and oldd are duplicate refer- ences 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) system call. The close-on-exec flag on the new file descriptor is unset. In dup2(), the value of the new descriptor newd is specified. If this descriptor is already in use and oldd != newd, the descriptor is first deallocated as if the close(2) system call had been used. If oldd is not a valid descriptor, then newd is not closed. If oldd == newd and oldd is a valid descriptor, then dup2() is successful, and does nothing. RETURN VALUES
These calls return the new file descriptor if successful; otherwise the value -1 is returned and the external variable errno is set to indi- cate the cause of the error. ERRORS
The dup() system call fails if: [EBADF] The oldd argument is not a valid active descriptor [EMFILE] Too many descriptors are active. The dup2() system call fails if: [EBADF] The oldd argument is not a valid active descriptor or the newd argument is negative or exceeds the maximum allowable descriptor number SEE ALSO
accept(2), close(2), fcntl(2), getdtablesize(2), open(2), pipe(2), socket(2), socketpair(2), dup3(3) STANDARDS
The dup() and dup2() system calls are expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1''). HISTORY
The dup() and dup2() functions appeared in Version 7 AT&T UNIX. BSD
June 1, 2013 BSD
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