Re: [RFC v1] man/man2/at.2: Add page

[Alejandro Colomar <alx+linux-man@kernel.org>]

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at(2)                 System Calls Manual                 at(2)

NAME
     at  -  identify  a file at directory specified by file de‐
     scriptor

SYNOPSIS
     #include <fcntl.h>  /* Definition of AT_* constants */

     long ...at(int dirfd, const char *path, ..., int flags, ...);

DESCRIPTION
     The *at() system calls perform an action on a file  speci‐
     fied by the combination of dirfd, path, and flags.

     If path is absolute, then dirfd is ignored.

     If  path  is  relative, then it is interpreted relative to
     the directory referred to by the file descriptor dirfd.

     If path is relative and dirfd is the special value  AT_FD‐
     CWD,  then  path  is  interpreted  relative to the current
     working directory of the calling process.

     The flags argument is a bit mask created by ORing together
     0 or more of the following values (some system  calls  may
     support more values).

     AT_EMPTY_PATH (since Linux 2.6.39)
            If path is an empty string, operate on the file re‐
            ferred  to  by  dirfd (which may have been obtained
            using the open(2)  O_PATH  flag).   In  this  case,
            dirfd can refer to any type of file, not just a di‐
            rectory.   If  dirfd is AT_FDCWD, the call operates
            on the current working  directory.   This  flag  is
            Linux-specific;  define  _GNU_SOURCE  to obtain its
            definition.

     AT_SYMLINK_NOFOLLOW
            If path is a symbolic link, do not dereference  it:
            instead operate on the link itself.

ERRORS
     Some common errors for these system calls:

     EACCES
            Search  permission  is denied on a component of the
            path prefix.  (See also path_resolution(7).)

     EBADF  path is relative but dirfd is neither AT_FDCWD  nor
            a valid file descriptor.

     EFAULT
            path points outside your accessible address space.

     EINVAL
            Invalid flags specified in flags.

     ELOOP  Too many symbolic links were encountered in resolv‐
            ing path.

     ENAMETOOLONG
            path is longer than PATH_MAX.

     ENOENT
            The file does not exist.

     ENOENT
            path  is  an empty string, but AT_EMPTY_PATH is not
            specified in flags.

     ENOENT
            A component of the path prefix is a  dangling  sym‐
            bolic link.

     ENOTDIR
            A component of the path prefix is not a directory.

     ENOTDIR
            path is relative and dirfd is a file descriptor re‐
            ferring to a file other than a directory.

VERSIONS
     On older kernels where these system calls are unavailable,
     the  glibc  wrapper  functions emulate them.  When path is
     relative, glibc constructs a pathname based  on  the  sym‐
     bolic  link in /proc/self/fd that corresponds to the dirfd
     argument.

STANDARDS
     TODO.

HISTORY
     TODO.

CAVEATS
     Most of these system calls are named with an 'at'  suffix,
     although some new system calls don't have this suffix.

SEE ALSO
     openat(2), path_resolution(7), symlink(7)

Linux man-pages (unreleased) (date)                       at(2)

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