Ubuntu Manpage: unlink, unlinkat - delete a name and possibly the file it refers to

NAME

       unlink, unlinkat - delete a name and possibly the file it refers to

SYNOPSIS

       #include <unistd.h>

       int unlink(const char *pathname);

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

       int unlinkat(int dirfd, const char *pathname, int flags);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       unlinkat():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE

DESCRIPTION

       unlink()  deletes  a name from the filesystem.  If that name was the last link to a file and no processes
       have the file open, the file is deleted and the space it was using is made available for reuse.

       If the name was the last link to a file but any processes still have the file open, the file will  remain
       in existence until the last file descriptor referring to it is closed.

       If the name referred to a symbolic link, the link is removed.

       If  the  name  referred to a socket, FIFO, or device, the name for it is removed but processes which have
       the object open may continue to use it.

   unlinkat()
       The unlinkat() system call operates in exactly the same way as either unlink() or rmdir(2) (depending  on
       whether or not flags includes the AT_REMOVEDIR flag) except for the differences described here.

       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 unlink() and rmdir(2) for a relative pathname).

       If  the  pathname given in pathname is relative and dirfd is the special value AT_FDCWD, then pathname is
       interpreted relative to the  current  working  directory  of  the  calling  process  (like  unlink()  and
       rmdir(2)).

       If the pathname given in pathname is absolute, then dirfd is ignored.

       flags  is a bit mask that can either be specified as 0, or by ORing together flag values that control the
       operation of unlinkat().  Currently only one such flag is defined:

       AT_REMOVEDIR
              By default, unlinkat() performs the equivalent of unlink() on pathname.  If the AT_REMOVEDIR  flag
              is specified, then performs the equivalent of rmdir(2) on pathname.

       See openat(2) for an explanation of the need for unlinkat().

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

EACCES Write access to the directory containing pathname is not allowed for the process's effective UID,
or one of the directories in pathname did not allow search permission. (See also
path_resolution(7).)

EBUSY The file pathname cannot be unlinked because it is being used by the system or another process;
for example, it is a mount point or the NFS client software created it to represent an active but
otherwise nameless inode ("NFS silly renamed").

EFAULT pathname points outside your accessible address space.

EIO An I/O error occurred.

EISDIR pathname refers to a directory. (This is the non-POSIX value returned by Linux since 2.1.132.)

ELOOP Too many symbolic links were encountered in translating pathname.

ENAMETOOLONG
pathname was too long.

ENOENT A component in pathname does not exist or is a dangling symbolic link, or pathname is empty.

ENOMEM Insufficient kernel memory was available.

ENOTDIR
A component used as a directory in pathname is not, in fact, a directory.

EPERM The system does not allow unlinking of directories, or unlinking of directories requires
privileges that the calling process doesn't have. (This is the POSIX prescribed error return; as
noted above, Linux returns EISDIR for this case.)

EPERM (Linux only)
The filesystem does not allow unlinking of files.

EPERM or EACCES
The directory containing pathname has the sticky bit (S_ISVTX) set and the process's effective UID
is neither the UID of the file to be deleted nor that of the directory containing it, and the
process is not privileged (Linux: does not have the CAP_FOWNER capability).

EROFS pathname refers to a file on a read-only filesystem.

The same errors that occur for unlink() and rmdir(2) can also occur for unlinkat(). The following
additional errors can occur for unlinkat():

EBADF dirfd is not a valid file descriptor.

EINVAL An invalid flag value was specified in flags.

EISDIR pathname refers to a directory, and AT_REMOVEDIR was not specified in flags.

ENOTDIR
pathname is relative and dirfd is a file descriptor referring to a file other than a directory.

VERSIONS

       unlinkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.

CONFORMING TO

       unlink(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.

       unlinkat(): POSIX.1-2008.

NOTES

   Glibc notes
       On older kernels where unlinkat() is unavailable, the glibc wrapper function falls back  to  the  use  of
       unlink(2)  or  rmdir(2).   When pathname is a relative pathname, glibc constructs a pathname based on the
       symbolic link in /proc/self/fd that corresponds to the dirfd argument.

BUGS

       Infelicities in the protocol underlying NFS can cause the unexpected disappearance  of  files  which  are
       still being used.

COLOPHON

       This page is part of release 4.04 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       http://www.kernel.org/doc/man-pages/.