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 *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:
               _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 to indicate the
       error.

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 since Linux
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).

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

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 pathname is relative but dirfd is neither AT_FDCWD nor 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 in Linux 2.6.16; library support was added in glibc 2.4.

STANDARDS

       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() 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.