NAME
openat - open a file relative to a directory file descriptor SYNOPSIS
#include
int openat(int dirfd, const char *pathname, int flags); int openat(int dirfd, const char *pathname, int flags, modet mode); Feature Test Macro Requirements for glibc (see featuretestmacros(7)): openat(): Since glibc 2.10: XOPENSOURCE >= 700 || POSIXCSOURCE >= 200809L Before glibc 2.10: ATFILESOURCE DESCRIPTION The openat() system call operates in exactly the same way as open(2), except for the differences described in this manual page. If the pathname given in pathname is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by open(2) for a relative pathname). If pathname is relative and dirfd is the special value ATFDCWD, then pathname is interpreted relative to the current working directory of the calling process (like open(2)). If pathname is absolute, then dirfd is ignored. RETURN VALUE On success, openat() returns a new file descriptor. On error, -1 is returned and errno is set to indicate the error. ERRORS The same errors that occur for open(2) can also occur for openat(). The following additional errors can occur for openat(): EBADF dirfd is not a valid file descriptor. ENOTDIR pathname is relative and dirfd is a file descriptor referring to a file other than a directory. VERSIONS openat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4. CONFORMING TO
POSIX.1-2008. A similar system call exists on Solaris. NOTES openat() and other similar system calls suffixed "at" are supported for two reasons. First, openat() allows an application to avoid race conditions that could occur when using open(2) to open files in directories other than the current working directory. These race conditions result from the fact that some component of the directory prefix given to open(2) could be changed in parallel with the call to open(2). Such races can be avoided by opening a file descriptor for the target directory, and then specifying that file descriptor as the dirfd argument of openat().
Second, openat() allows the implementation of a per-thread "current working directory", via file descriptor(s) maintained by the applica‐ tion. (This functionality can also be obtained by tricks based on the use of /proc/self/fd/dirfd, but less efficiently.) SEE ALSO faccessat(2), fchmodat(2), fchownat(2), fstatat(2), futimesat(2), linkat(2), mkdirat(2), mknodat(2), open(2), readlinkat(2), renameat(2), symlinkat(2), unlinkat(2), utimensat(2), mkfifoat(3), pathresolu‐ tion(7) COLOPHON
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Linux 2012-05-04 OPENAT(2)