man-pages/man2/unlink.2

.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\"             and Copyright (C) 1993 Ian Jackson
.\"             and Copyright (C) 2006, 2014 Michael Kerrisk.
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-09-08 by Arnt Gulbrandsen <agulbra@troll.no>
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2001-05-17 by aeb
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.TH UNLINK 2 2021-08-27 "Linux" "Linux Programmer's Manual"
.SH NAME
unlink, unlinkat \- delete a name and possibly the file it refers to
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.PP
.BI "int unlink(const char *" pathname );
.PP
.BR "#include <fcntl.h>           " "/* Definition of " AT_* " constants */"
.B #include <unistd.h>
.PP
.BI "int unlinkat(int " dirfd ", const char *" pathname ", int " flags );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR unlinkat ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _ATFILE_SOURCE
.fi
.SH DESCRIPTION
.BR 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.
.PP
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.
.PP
If the name referred to a symbolic link, the link is removed.
.PP
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.
.SS unlinkat()
The
.BR unlinkat ()
system call operates in exactly the same way as either
.BR unlink ()
or
.BR rmdir (2)
(depending on whether or not
.I flags
includes the
.B AT_REMOVEDIR
flag)
except for the differences described here.
.PP
If the pathname given in
.I pathname
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR unlink ()
and
.BR rmdir (2)
for a relative pathname).
.PP
If the pathname given in
.I pathname
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I pathname
is interpreted relative to the current working
directory of the calling process (like
.BR unlink ()
and
.BR rmdir (2)).
.PP
If the pathname given in
.I pathname
is absolute, then
.I dirfd
is ignored.
.PP
.I flags
is a bit mask that can either be specified as 0, or by ORing
together flag values that control the operation of
.BR unlinkat ().
Currently, only one such flag is defined:
.TP
.B AT_REMOVEDIR
By default,
.BR unlinkat ()
performs the equivalent of
.BR unlink ()
on
.IR pathname .
If the
.B AT_REMOVEDIR
flag is specified, then
performs the equivalent of
.BR rmdir (2)
on
.IR pathname .
.PP
See
.BR openat (2)
for an explanation of the need for
.BR unlinkat ().
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EACCES
Write access to the directory containing
.I pathname
is not allowed for the process's effective UID, or one of the
directories in
.I pathname
did not allow search permission.
(See also
.BR path_resolution (7).)
.TP
.BR EBUSY
The file
.I 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").
.TP
.B EFAULT
.I pathname
points outside your accessible address space.
.TP
.B EIO
An I/O error occurred.
.TP
.B EISDIR
.I pathname
refers to a directory.
(This is the non-POSIX value returned by Linux since 2.1.132.)
.TP
.B ELOOP
Too many symbolic links were encountered in translating
.IR pathname .
.TP
.B ENAMETOOLONG
.IR pathname " was too long."
.TP
.B ENOENT
A component in
.I pathname
does not exist or is a dangling symbolic link, or
.I pathname
is empty.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component used as a directory in
.I pathname
is not, in fact, a directory.
.TP
.B 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
.B EISDIR
for this case.)
.TP
.BR EPERM " (Linux only)"
The filesystem does not allow unlinking of files.
.TP
.BR EPERM " or " EACCES
The directory containing
.I pathname
has the sticky bit
.RB ( 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
.B CAP_FOWNER
capability).
.TP
.B EPERM
The file to be unlinked is marked immutable or append-only.
(See
.BR ioctl_iflags (2).)
.TP
.B EROFS
.I pathname
refers to a file on a read-only filesystem.
.PP
The same errors that occur for
.BR unlink ()
and
.BR rmdir (2)
can also occur for
.BR unlinkat ().
The following additional errors can occur for
.BR unlinkat ():
.TP
.B EBADF
.I pathname
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EINVAL
An invalid flag value was specified in
.IR flags .
.TP
.B EISDIR
.I pathname
refers to a directory, and
.B AT_REMOVEDIR
was not specified in
.IR flags .
.TP
.B ENOTDIR
.I pathname
is relative and
.I dirfd
is a file descriptor referring to a file other than a directory.
.SH VERSIONS
.BR unlinkat ()
was added to Linux in kernel 2.6.16;
library support was added to glibc in version 2.4.
.SH CONFORMING TO
.BR unlink ():
SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
.\" SVr4 documents additional error
.\" conditions EINTR, EMULTIHOP, ETXTBSY, ENOLINK.
.PP
.BR unlinkat ():
POSIX.1-2008.
.SH NOTES
.SS Glibc notes
On older kernels where
.BR unlinkat ()
is unavailable, the glibc wrapper function falls back to the use of
.BR unlink ()
or
.BR rmdir (2).
When
.I pathname
is a relative pathname,
glibc constructs a pathname based on the symbolic link in
.IR /proc/self/fd
that corresponds to the
.IR dirfd
argument.
.SH BUGS
Infelicities in the protocol underlying NFS can cause the unexpected
disappearance of files which are still being used.
.SH SEE ALSO
.BR rm (1),
.BR unlink (1),
.BR chmod (2),
.BR link (2),
.BR mknod (2),
.BR open (2),
.BR rename (2),
.BR rmdir (2),
.BR mkfifo (3),
.BR remove (3),
.BR path_resolution (7),
.BR symlink (7)