xref: /freebsd/lib/libsys/unlink.2 (revision 8269e7673cf033aba67dab8264fe719920c70f87)

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.Dd February 23, 2021
.Dt UNLINK 2
.Os
.Sh NAME
.Nm unlink ,
.Nm unlinkat ,
.Nm funlinkat
.Nd remove directory entry
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn unlink "const char *path"
.Ft int
.Fn unlinkat "int dfd" "const char *path" "int flag"
.Ft int
.Fn funlinkat "int dfd" "const char *path" "int fd" "int flag"
.Sh DESCRIPTION
The
.Fn unlink
system call
removes the link named by
.Fa path
from its directory and decrements the link count of the
file which was referenced by the link.
If that decrement reduces the link count of the file
to zero,
and no process has the file open, then
all resources associated with the file are reclaimed.
If one or more process have the file open when the last link is removed,
the link is removed, but the removal of the file is delayed until
all references to it have been closed.
The
.Fa path
argument
may not be a directory.
.Pp
The
.Fn unlinkat
system call is equivalent to
.Fn unlink
or
.Fn rmdir
except in the case where
.Fa path
specifies a relative path.
In this case the directory entry to be removed is determined
relative to the directory associated with the file descriptor
.Fa dfd
instead of the current working directory.
.Pp
The values for
.Fa flag
are constructed by a bitwise-inclusive OR of flags from the following list,
defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_REMOVEDIR
Remove the directory entry specified by
.Fa fd
and
.Fa path
as a directory, not a normal file.
.It Dv AT_RESOLVE_BENEATH
Only walk paths below the directory specified by the
.Ar fd
descriptor.
See the description of the
.Dv O_RESOLVE_BENEATH
flag in the
.Xr open 2
manual page.
.El
.Pp
If
.Fn unlinkat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fa unlink
or
.Fa rmdir
respectively, depending on whether or not the
.Dv AT_REMOVEDIR
bit is set in flag.
.Pp
The
.Fn funlinkat
system call can be used to unlink an already-opened file, unless that
file has been replaced since it was opened.
It is equivalent to
.Fn unlinkat
in the case where
.Fa path
is already open as the file descriptor
.Fa fd .
Otherwise, the path will not be removed and an error will be returned.
The
.Fa fd
can be set the
.Dv FD_NONE .
In that case
.Fn funlinkat
behaves exactly like
.Fn unlinkat .
.Sh RETURN VALUES
.Rv -std unlink
.Sh ERRORS
The
.Fn unlink
succeeds unless:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er EISDIR
The named file is a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er EACCES
Write permission is denied on the directory containing the link
to be removed.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EPERM
The named file is a directory.
.It Bq Er EPERM
The named file has its immutable, undeletable or append-only flag set, see the
.Xr chflags 2
manual page for more information.
.It Bq Er EPERM
The parent directory of the named file has its immutable or append-only flag
set.
.It Bq Er EPERM
The directory containing the file is marked sticky,
and neither the containing directory nor the file to be removed
are owned by the effective user ID.
.It Bq Er EIO
An I/O error occurred while deleting the directory entry
or deallocating the inode.
.It Bq Er EINTEGRITY
Corrupted data was detected while reading from the file system.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er EFAULT
The
.Fa path
argument
points outside the process's allocated address space.
.It Bq Er ENOSPC
On file systems supporting copy-on-write or snapshots, there was not enough
free space to record metadata for the delete operation of the file.
.El
.Pp
In addition to the errors returned by the
.Fn unlink ,
the
.Fn unlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er ENOTEMPTY
The
.Fa flag
parameter has the
.Dv AT_REMOVEDIR
bit set and the
.Fa path
argument names a directory that is not an empty directory,
or there are hard links to the directory other than dot or
a single entry in dot-dot.
.It Bq Er ENOTDIR
The
.Fa flag
parameter has the
.Dv AT_REMOVEDIR
bit set and
.Fa path
does not name a directory.
.It Bq Er EINVAL
The value of the
.Fa flag
argument is not valid.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.It Bq Er ENOTCAPABLE
.Fa path
is an absolute path,
or contained a ".." component leading to a
directory outside of the directory hierarchy specified by
.Fa fd ,
and the process is in capability mode or the
.Dv AT_RESOLVE_BENEATH
flag was specified.
.El
.Pp
In addition to the errors returned by
.Fn unlinkat ,
.Fn funlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EDEADLK
The file descriptor is not associated with the path.
.El
.Sh SEE ALSO
.Xr chflags 2 ,
.Xr close 2 ,
.Xr link 2 ,
.Xr rmdir 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn unlinkat
system call follows The Open Group Extended API Set 2 specification.
.Sh HISTORY
The
.Fn unlink
function appeared in
.At v1 .
The
.Fn unlinkat
system call appeared in
.Fx 8.0 .
The
.Fn funlinkat
system call appeared in
.Fx 13.0 .
.Pp
The
.Fn unlink
system call traditionally allows the super-user to unlink directories which
can damage the file system integrity.
This implementation no longer permits it.