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@(#)close.2 6.3 (Berkeley) 5/22/86
#include <unistd.h> int close(int d)
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 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 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);
15 [EBADF] D is not an active descriptor.