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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       int unlink(const char *path);

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

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

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

       unlinkat():
           Since glibc 2.10:
               _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  path 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  path  is  relative  and dirfd is the special value AT_FDCWD, then path is interpreted relative to the
       current working directory of the calling process (like unlink() and rmdir(2)).

       If path 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 path.  If the AT_REMOVEDIR flag is
              specified, it performs the equivalent of rmdir(2) on path.

       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 to indicate the error.

ERRORS

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

EBUSY path 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 path points outside your accessible address space.

EIO An I/O error occurred.

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

ELOOP Too many symbolic links were encountered in translating path.

ENAMETOOLONG
path was too long.

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

ENOMEM Insufficient kernel memory was available.

ENOTDIR
A component used as a directory in path 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 path 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).

EPERM The file to be unlinked is marked immutable or append-only. (See FS_IOC_SETFLAGS(2const).)

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

EINVAL An invalid flag value was specified in flags.

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

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

STANDARDS

       POSIX.1-2008.

HISTORY

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

       unlinkat()
              POSIX.1-2008.  Linux 2.6.16, glibc 2.4.

   glibc
       On older kernels where unlinkat() is unavailable, the glibc wrapper function falls back  to  the  use  of
       unlink()  or  rmdir(2).  When path is relative, 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.